# CVE-2026-104259: ModSecurity: removeComments Transformation Fails to Strip Adjacent Comments, Enabling WAF Rule Bypass

Status: published. Published: 2026-11-09. Updated: 2026-11-09.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- owasp-modsecurity / ModSecurity: < 2.9.15 (affected); >= 3.0.0, < 3.0.17 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 5.4 (medium); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-670

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-qrch-pjfr-9g47 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/owasp-modsecurity/ModSecurity/commit/264f348ae1823cb71cead3650b74c165678a1d46 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/owasp-modsecurity/ModSecurity/commit/49a65f471d3130b91f7fff9bfac9fe8dd9b97c44 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v2.9.15 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-104259; retrieved 2026-11-09; source updated 2026-11-09

Revision: c56bfdbc74bfd2158e69ebd226b7b46f88843cdb5e43b09bb58d03d6a84b0441

Canonical: https://y2.dev/cve/CVE-2026-104259

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