sanitize

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.

Patches

Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.

Workarounds

Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.

Details

The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.

References

• Release Notes

Credit

Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!

When HTML is sanitized using Sanitize's "relaxed" config or a custom config that allows certain elements, some content in a <math> or <svg> element may not be sanitized correctly even if math and svg are not in the allowlist.

You are likely to be vulnerable to this issue if you use Sanitize's relaxed config or a custom config that allows one or more of the following HTML elements:

• iframe
• math
• noembed
• noframes
• noscript
• plaintext
• script
• style
• svg
• xmp

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.

Releases

This problem has been fixed in Sanitize 5.2.1.

Workarounds

If upgrading is not possible, a workaround is to override the default value of Sanitize's :remove_contents config option with the following value, which ensures that the contents of math and svg elements (among others) are removed entirely when those elements are not in the allowlist:

%w[iframe math noembed noframes noscript plaintext script style svg xmp]

For example, if you currently use Sanitize's relaxed config, you can create a custom config object that overrides the default value of :remove_contents like this:

custom_config = Sanitize::Config.merge(
  Sanitize::Config::RELAXED,
  :remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)

You would then pass this custom config to Sanitize when sanitizing HTML.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Sanitize repo.
• See Sanitize's security policy.

Credits

Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.

References

• GHSA-p4x4-rw2p-8j8m
• CVE-2020-4054
• https://github.com/rgrove/sanitize/releases/tag/v5.2.1

When Sanitize <= 4.6.2 is used in combination with libxml2 >= 2.9.2, a specially crafted HTML fragment can cause libxml2 to generate improperly escaped output, allowing non-whitelisted attributes to be used on whitelisted elements.

This can allow HTML and JavaScript injection, which could result in XSS if Sanitize's output is served to browsers.

Impact

Using carefully crafted input, an attacker may be able to sneak arbitrary HTML and CSS through Sanitize >= 3.0.0, < 6.0.2 when Sanitize is configured to use the built-in "relaxed" config or when using a custom config that allows style elements and one or more CSS at-rules. This could result in XSS (cross-site scripting) or other undesired behavior when the malicious HTML and CSS are rendered in a browser.

Patches

Sanitize >= 6.0.2 performs additional escaping of CSS in style element content, which fixes this issue.

Workarounds

Users who are unable to upgrade can prevent this issue by using a Sanitize config that doesn't allow style elements, using a Sanitize config that doesn't allow CSS at-rules, or by manually escaping the character sequence </ as <\/ in style element content.

Credit

This issue was found by @cure53 during an audit of a project that uses Sanitize and was reported by one of that project's maintainers. Thank you!