CVE-2026-21876

Name	CVE-2026-21876
Description	The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 4.22.0 and 3.3.8, the current rule 922110 has a bug when processing multipart requests with multiple parts. When the first rule in a chain iterates over a collection (like `MULTIPART_PART_HEADERS`), the capture variables (`TX:0`, `TX:1`) get overwritten with each iteration. Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset. Versions 4.22.0 and 3.3.8 patch the issue.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1125084

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
modsecurity-crs (PTS)	bullseye	3.3.0-1+deb11u1	vulnerable
	bullseye (security)	3.3.4-1~deb11u1	vulnerable
	bookworm	3.3.4-1	vulnerable
	forky, sid, trixie	3.3.7-1	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
modsecurity-crs	source	(unstable)	(unfixed)			1125084

Notes

https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5
Fixed by (merge): https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83 (v3.3.8)
Fixed by (merge): https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6 (v4.22.0)