Incorrect bad URL tokenization in Crass enables CSS sanitizer bypass
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- Passive
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- None · None · None
- Fix status
- Partial Red Hat: 2 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat.
Summary
Crass, a Ruby CSS parser, is affected in versions before 1.0.8. While consuming the remnants of a bad URL, Crass treats a closing parenthesis after an escaped backslash as escaped, so it keeps declarations, style rules, or at-rules that browsers treat as live CSS (CWE-436). A sanitizer that reserializes such untrusted CSS without rejecting the bad URL can allow UI redress, external resource loading, or CSS-based data exfiltration, but this does not enable script execution in modern browsers.
Written with Claude Haiku 5.5 from the sources below · 2026-11-03
Description from the CNA
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| rgrove | crass | before 1.0.8 | 1.0.8 | Patch available | CNA |
| — | crass (RubyGems) | before 1.0.8 | 1.0.8 | Patch available | GHSA-pq4g-8rxf-4g29 |
- crass Vendorrgrove Affected before 1.0.8 Fixed in 1.0.8 Patch available CNA
- crass (RubyGems) Vendor— Affected before 1.0.8 Fixed in 1.0.8 Patch available GHSA-pq4g-8rxf-4g29
Remediation
Upgrade crass to version 1.0.8, the fixed version for both the rgrove crass and RubyGems crass entries. Red Hat has no fix plan available for Red Hat 3scale API Management Platform 2 or Red Hat Satellite 6.
Written with Claude Haiku 5.5 from the sources below · 2026-11-03
- Fix · CNA crass (rgrove) Fixed in 1.0.8
- Fix · GHSA-pq4g-8rxf-4g29 crass (RubyGems) Fixed in 1.0.8 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat 3scale API Management Platform 2 | Affected | No fix yet: Fix deferred |
| Red Hat Satellite 6 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-27 Threatist record created from CVE-2026-116695
- 2026-10-28 Alias added: GHSA-pq4g-8rxf-4g29
- 2026-10-28 Fix available: RubyGems/[email protected] · GHSA-pq4g-8rxf-4g29
- 2026-10-28 CVSS score added · GHSA-pq4g-8rxf-4g29
- 2026-10-28 Weakness changed · GHSA-pq4g-8rxf-4g29
- 2026-10-28 6 new references · GHSA-pq4g-8rxf-4g29
- 2026-10-29 Affected versions changed · Red Hat
- 2026-10-29 CVSS score added · Red Hat
- 2026-11-03 CISA SSVC decision points changed
References
Other 5
- https://github.com/rgrove/crass/security/advisories/GHSA-pq4g-8rxf-4g29
- https://github.com/rgrove/crass/commit/689fc45c632fdf3803b2f4e844ffc9cca3b08f34
- https://github.com/rgrove/crass/releases/tag/v1.0.8
- https://github.com/rgrove/crass
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/crass/GHSA-pq4g-8rxf-4g29.yml
More rgrove vulnerabilities
- TI-2026-83291 Large numeric exponents in Crass CSS parser exhaust CPU and memory CVSS 4.0HIGH 8.9
- TI-2020-03543 Cross-site Scripting in Sanitize CVSS 3.1HIGH 7.3
- TI-2018-02737 Cross-site scripting in Ryan Grove sanitize CVSS 3.0HIGH 7.5
- TI-2026-83327 Uncontrolled recursion in Crass CSS parser exhausts stack or memory CVSS 4.0MEDIUM 6.3
- TI-2023-18617 Sanitize vulnerable to Cross-site Scripting via insufficient neutralization of `style` element content CVSS 3.1HIGH 7.1
- TI-2026-83329 Superlinear CPU use in Crass CSS parser with non-ASCII input CVSS 4.0MEDIUM 6.3
Sources
- CVE-2026-116695 · CVE Program
- CVE-2026-116695 · NVD
- FIRST EPSS
- GHSA-pq4g-8rxf-4g29 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-116695 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences