setuptools

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.

Details

File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:

# setuptools/command/egg_info.py  (FileList.global_exclude)
def global_exclude(self, pattern):
    match = translate_pattern(os.path.join('**', pattern))   # fnmatch.translate -> regex, no NFC/NFD
    return self._remove_files(match.match)                   # byte-level regex over raw os.walk names

A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.

A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.

Impact

MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.

Proof of concept

With a project containing MANIFEST.in:

global-include *.txt *.json
global-exclude secret_café.txt    # rule saved NFC

and an on-disk file secret_café.txt written in NFD, python -m build --sdist packs the secret file into the resulting .tar.gz, while an ASCII control file excluded by the same directive is correctly dropped — isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.

Remediation

Normalize both the walked path and each MANIFEST.in pattern to a single canonical form before matching, in both setuptools/command/egg_info.py (FileList) and the vendored setuptools/_distutils/filelist.py. For an exclusion list, err toward excluding more, and document that MANIFEST.in matching is normalization-insensitive on macOS.

Credit

Reported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.

Details

File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:

# setuptools/command/egg_info.py  (FileList.global_exclude)
def global_exclude(self, pattern):
    match = translate_pattern(os.path.join('**', pattern))   # fnmatch.translate -> regex, no NFC/NFD
    return self._remove_files(match.match)                   # byte-level regex over raw os.walk names

A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.

A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.

Impact

MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.

Proof of concept

With a project containing MANIFEST.in:

global-include *.txt *.json
global-exclude secret_café.txt    # rule saved NFC

and an on-disk file secret_café.txt written in NFD, python -m build --sdist packs the secret file into the resulting .tar.gz, while an ASCII control file excluded by the same directive is correctly dropped — isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.

Remediation

Normalize both the walked path and each MANIFEST.in pattern to a single canonical form before matching, in both setuptools/command/egg_info.py (FileList) and the vendored setuptools/_distutils/filelist.py. For an exclusion list, err toward excluding more, and document that MANIFEST.in matching is normalization-insensitive on macOS.

Credit

Reported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.

Details

File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:

# setuptools/command/egg_info.py  (FileList.global_exclude)
def global_exclude(self, pattern):
    match = translate_pattern(os.path.join('**', pattern))   # fnmatch.translate -> regex, no NFC/NFD
    return self._remove_files(match.match)                   # byte-level regex over raw os.walk names

A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.

A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.

Impact

MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.

Proof of concept

With a project containing MANIFEST.in:

global-include *.txt *.json
global-exclude secret_café.txt    # rule saved NFC

and an on-disk file secret_café.txt written in NFD, python -m build --sdist packs the secret file into the resulting .tar.gz, while an ASCII control file excluded by the same directive is correctly dropped — isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.

Remediation

Normalize both the walked path and each MANIFEST.in pattern to a single canonical form before matching, in both setuptools/command/egg_info.py (FileList) and the vendored setuptools/_distutils/filelist.py. For an exclusion list, err toward excluding more, and document that MANIFEST.in matching is normalization-insensitive on macOS.

Credit

Reported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.

Summary

A path traversal vulnerability in PackageIndex was fixed in setuptools version 78.1.1

Details

    def _download_url(self, url, tmpdir):
        # Determine download filename
        #
        name, _fragment = egg_info_for_url(url)
        if name:
            while '..' in name:
                name = name.replace('..', '.').replace('\\', '_')
        else:
            name = "__downloaded__"  # default if URL has no path contents

        if name.endswith('.[egg.zip](http://egg.zip/)'):
            name = name[:-4]  # strip the extra .zip before download

 -->       filename = os.path.join(tmpdir, name)

Here: https://github.com/pypa/setuptools/blob/6ead555c5fb29bc57fe6105b1bffc163f56fd558/setuptools/package_index.py#L810C1-L825C88

os.path.join() discards the first argument tmpdir if the second begins with a slash or drive letter. name is derived from a URL without sufficient sanitization. While there is some attempt to sanitize by replacing instances of '..' with '.', it is insufficient.

Risk Assessment

As easy_install and package_index are deprecated, the exploitation surface is reduced. However, it seems this could be exploited in a similar fashion like https://github.com/advisories/GHSA-r9hx-vwmv-q579, and as described by POC 4 in https://github.com/advisories/GHSA-cx63-2mw6-8hw5 report: via malicious URLs present on the pages of a package index.

Impact

An attacker would be allowed to write files to arbitrary locations on the filesystem with the permissions of the process running the Python code, which could escalate to RCE depending on the context.

References

https://huntr.com/bounties/d6362117-ad57-4e83-951f-b8141c6e7ca5 https://github.com/pypa/setuptools/issues/4946

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.

Details

File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:

# setuptools/command/egg_info.py  (FileList.global_exclude)
def global_exclude(self, pattern):
    match = translate_pattern(os.path.join('**', pattern))   # fnmatch.translate -> regex, no NFC/NFD
    return self._remove_files(match.match)                   # byte-level regex over raw os.walk names

A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.

A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.

Impact

MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.

Proof of concept

With a project containing MANIFEST.in:

global-include *.txt *.json
global-exclude secret_café.txt    # rule saved NFC

and an on-disk file secret_café.txt written in NFD, python -m build --sdist packs the secret file into the resulting .tar.gz, while an ASCII control file excluded by the same directive is correctly dropped — isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.

Remediation

Normalize both the walked path and each MANIFEST.in pattern to a single canonical form before matching, in both setuptools/command/egg_info.py (FileList) and the vendored setuptools/_distutils/filelist.py. For an exclusion list, err toward excluding more, and document that MANIFEST.in matching is normalization-insensitive on macOS.

Credit

Reported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence.

### Impact

A crafted wheel can cause setuptools to create a fixed-content
`__init__.py` outside the intended installation directory at a
filesystem path influenced by the wheel, with the permissions of the
process performing the installation.

The demonstrated reproduction required the target parent directory to
already exist.

Summary

When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.

Details

File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:

# setuptools/command/egg_info.py  (FileList.global_exclude)
def global_exclude(self, pattern):
    match = translate_pattern(os.path.join('**', pattern))   # fnmatch.translate -> regex, no NFC/NFD
    return self._remove_files(match.match)                   # byte-level regex over raw os.walk names

A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.

A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.

Impact

MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.

Proof of concept

With a project containing MANIFEST.in:

global-include *.txt *.json
global-exclude secret_café.txt    # rule saved NFC

and an on-disk file secret_café.txt written in NFD, python -m build --sdist packs the secret file into the resulting .tar.gz, while an ASCII control file excluded by the same directive is correctly dropped — isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.

Remediation

Normalize both the walked path and each MANIFEST.in pattern to a single canonical form before matching, in both setuptools/command/egg_info.py (FileList) and the vendored setuptools/_distutils/filelist.py. For an exclusion list, err toward excluding more, and document that MANIFEST.in matching is normalization-insensitive on macOS.

Credit

Reported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.