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