by Kastro CVE-2026-21876
coreruleset coreruleset — OWASP CRS has multipart bypass using multiple content-type parts
Description · from the CVE record
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
ProductAffectedFixed inSource
coreruleset< 4.22.0–CNA
coreruleset< 3.3.8–CNA
Scores by source
GitHub_M (CNA)9.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: partial