CVE-2026-21876

9.3 CRITICAL
Published: January 08, 2026 Modified: February 23, 2026
View on NVD

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.

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CVSS v3.x Details

0.0 Low Medium High Critical 10.0
Vector String
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N

References to Advisories, Solutions, and Tools

Patch Vendor Advisory Exploit Third Party Advisory
https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8
Source: security-advisories@github.com
Product Release Notes
https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0
Source: security-advisories@github.com
Product Release Notes
https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5
Source: security-advisories@github.com
Vendor Advisory Exploit

5 reference(s) from NVD

Quick Stats

CVSS v3 Score
9.3 / 10.0
EPSS (Exploit Probability)
0.1%
20th percentile
Exploitation Status
Not in CISA KEV

Weaknesses (CWE)

Affected Vendors

owasp