Crass is a Ruby CSS parser that is compliant with the CSS Syntax Level 3 specification. Prior to 1.0.8, Crass incorrectly treats a closing parenthesis after an escaped backslash as escaped while consuming the remnants of a bad URL. Crass therefore keeps declarations, style rules, or at-rules inside a bad URL token even though a browser treats them as live CSS.
A sanitizer that parses untrusted CSS with Crass and reserializes it without rejecting the bad URL can allow CSS used for UI redress, external resource loading, or CSS-based data exfiltration, but this issue does not enable script execution in modern browsers. This issue is fixed in version 1.0.8.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
None
No additional conditions
Privileges Required
None
No privileges needed
User Interaction
Passive
Minimal interaction
Impact Assessment
Confidentiality
None
No data leak
Integrity
None
No data modification
Availability
None
No disruption
CVSS Vector v4.0
Weakness Type (CWE)
Vulnerable Products
rgrove:crass
References 3
https://github.com/rgrove/crass/security/advisories/GHSA-pq4g-8rxf-4g29
https://github.com/rgrove/crass/security/advisories/GHSA-pq4g-8rxf-4g29
https://github.com/rgrove/crass/commit/689fc45c632fdf3803b2f4e844ffc9cca3b08f34
https://github.com/rgrove/crass/commit/689fc45c632fdf3803b2f4e844ffc9cca3b08f34
https://github.com/rgrove/crass/releases/tag/v1.0.8
https://github.com/rgrove/crass/releases/tag/v1.0.8