req

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's multipart form encoder interpolates the per-part name, filename, and content_type directly into the part headers without escaping. An attacker who can influence any of those values can inject CRLF-separated header lines, smuggle additional form fields, or prepend a whole extra part into the request the victim service sends downstream.

Details

Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part header iodata by concatenating the three caller-supplied strings verbatim into content-disposition: form-data; name="<name>"; filename="<filename>" and content-type: <content_type>. There is no CRLF stripping, no quote escaping, and no validation. A value containing "\r\n closes the surrounding quoted value and starts a new header line; an additional \r\n--<boundary> terminates the current part and lets the attacker prepend a smuggled part.

The flaw is reachable through every supported way of supplying a part. It is especially easy to hit when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. RFC 7578 / WHATWG form-data requires percent-encoding ", CR, and LF in these fields; the fix adopts that behavior.

PoC

1. Construct a malicious filename such as harmless.txt"\r\nX-Smuggled: marker\r\nContent-Disposition: form-data; name="pwned.
2. Call Req.post!(url, form_multipart: [upload: {"benign body", filename: <malicious>, content_type: "text/plain"}]).
3. The emitted multipart body contains a real X-Smuggled: header line and an extra Content-Disposition for name="pwned", alongside Req's legitimate headers.

Impact

HTTP request smuggling / multipart parameter smuggling in the HTTP client. Any application using Req to send form_multipart requests where any of name, filename, or content_type can be influenced by an untrusted source is affected, most commonly upload proxies and re-uploaders that derive filename from Path.basename/1 on a user-controlled path.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.decompress_body/1 walks the content-encoding header and chains :zlib / :brotli / :ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip, … inflates through multiple layers without bound.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

1. Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
2. From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
3. decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.