CVE-2026-104259 json
ModSecurity: removeComments Transformation Fails to Strip Adjacent Comments, Enabling WAF Rule Bypass
published last mo. modified yesterday also EUVD-2026-120509 , GHSA-qrch-pjfr-9g47
Unreviewed: the maintainers' own advisory
Published by the maintainers on their GitHub repository owasp-modsecurity/ModSecurity. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.
- cvss
- 5.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 12%
- public exploits
- 0
- none known
Summary
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Prior to 2.9.15 and 3.0.17, msre_fn_removeComments_execute in apache2/re_tfns.c and inplace() in src/actions/transformations/remove_comments.cc implement t:removeComments by copying the character immediately after a comment terminator without re-evaluating it. Adjacent comments can therefore leave a later comment in the transformed value, allowing inline-comment obfuscation to bypass rules that depend on comment stripping. When a comment terminator is the final content, the same copy reads one byte beyond the input buffer. This issue is fixed in versions 2.9.15 and 3.0.17.
Patch / fix
Is CVE-2026-104259 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- yesterday
Exploit prediction
0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N |
Affected products
- owasp-modsecurity ModSecurity
Classification
- Weakness
-
- CWE-670 Always-Incorrect Control Flow Implementation
References
- github.com /owasp-modsecurity/ModSecurity/commit/264f348ae1823cb71cead3650b74c165678a1d46
- github.com /owasp-modsecurity/ModSecurity/commit/49a65f471d3130b91f7fff9bfac9fe8dd9b97c44
-
github.com
/owasp-modsecurity/ModSecurity/security/advisories/GHSA-qrch-pjfr-9g47
advisory
- github.com /owasp-modsecurity/ModSecurity/releases/tag/v2.9.15
- github.com /owasp-modsecurity/ModSecurity/releases/tag/v3.0.17
Sources
- CVE List CVE-2026-104259
- NVD CVE-2026-104259
- Maintainer advisory GHSA-qrch-pjfr-9g47
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of owasp-modsecurity/ModSecurity published their own advisory on GitHub. Reviewed sources take precedence over it.