CVE-2026-21876

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.

Affected products

Coraza, Debian, Modsecurity, Owasp Core Rule Set

Owasp Owasp Modsecurity Core Rule Set

< 3.3.8, 4.22.0

Fix

Available

CVSS 3.1

9.3 CRITICAL

EPSS

13.6% (96th percentile)

Weakness

CWE-794

NVD status

Modified

Published

2026-01-08