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CVE-2026-21876

Severity
CRITICAL
CVSS
9.3
EPSS
0.13346
Risk score
41.87
CISA KEV
No
PoC
No
Published
2026-01-08
Modified
2026-04-09
First seen
2026-08-07
Aliases
EUVD-2026-1669
Products
coreruleset:coreruleset < 3.3.8, coreruleset:coreruleset < 4.22.0
Sources
euvd EUVD-2026-1669

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.

References