CVE-2026-21876

Public on 2026-01-08
Modified on 2026-01-09
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.
Severity
Important severity
Important
See what this means
CVSS v3 Base Score
8.6
See breakdown

Affected Packages

Platform Package Release Date Advisory Status
Amazon Linux 2 - Core mod_security_crs Not Affected
Amazon Linux 2023 mod_security_crs Pending Fix

CVSS Scores

Score Type Score Vector
Amazon Linux CVSSv3 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N