Sanitize vulnerable to Cross-site Scripting via insufficient neutralization of `style` element content
Date: 2023-07
Affected: rubygems/sanitize
Attack vector: xss
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2023-36823
CWE: CWE-79
CVSS: 7.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L)

### 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!


Mitigations:

Architectural layers (MAESTRO):