CVE-2026-21876

Publication date 9 January 2026

Last updated 9 January 2026

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

9.3 · Critical

Score breakdown

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.

Status

Package Ubuntu Release Status
modsecurity-crs 25.10 questing
Needs evaluation
25.04 plucky
Needs evaluation
24.04 LTS noble
Needs evaluation
22.04 LTS jammy
Needs evaluation
20.04 LTS focal
Needs evaluation
18.04 LTS bionic
Needs evaluation
16.04 LTS xenial
Needs evaluation

Severity score breakdown

Parameter Value
Base score 9.3 · Critical
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Scope Changed
Confidentiality High
Integrity impact Low
Availability impact None
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N

References

Other references