CVE-2026-21876
modsecurity-crs - security update
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.
How to fix CVE-2026-21876
To remediate CVE-2026-21876, upgrade the affected package to a fixed version below.
- —upgrade to 3.3.4-1~deb11u2 or later
- —upgrade to 3.3.4-1+deb12u1 or later
Is CVE-2026-21876 being exploited?
Low — EPSS is 4.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 3.3.4-1~deb11u2
- from 0, < 3.3.4-1+deb12u1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N |