vulnerability / NVI-00009122 / Revision 3
Crass: Incorrect tokenization of bad URLs enables CSS sanitizer bypass
GitHub lists this reviewed advisory for crass. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
0.353%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.29027. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
crass
source listed<= 1.0.7
## Summary Crass's tokenizer didn't terminate a bad URL token at a `)` that followed an escaped backslash (`\\`). As a result, Crass consumed more input as part of the bad URL than a spec-compliant browser does. CSS sanitizers that parse untrusted CSS with Crass and re-emit it could be tricked into passing through declarations, style rules, or at-rules (including `@import`) that the sanitizer would otherwise have removed, but that a browser would then parse and apply. ## Details While consuming the remnants of a bad URL (CSS Syntax Level 3, §4.3.15), Crass checked whether the *previously consumed* code point and the next code point formed a valid escape, in addition to checking the next two unconsumed code points. After an escaped backslash, the previously consumed code point is a backslash, so a following `)` was incorrectly treated as escaped and the bad URL token continued until the next unescaped `)` or the end of the input. Browsers terminate the bad URL at that `)`, so everything Crass treated as part of the bad URL is live CSS to a browser. This bug has existed in every released version of Crass. ## Impact Crass by itself only mis-tokenizes input. The security impact
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-pq4g-8rxf-4g29 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-116695 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.