OWASP CRS has multipart bypass using multiple content-type parts

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Summary

CVECVE-2026-21876
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-01-08 14:15:57 UTC
Updated2026-04-09 16:16:26 UTC
DescriptionThe 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Problem Types: CWE-794 | CWE-794 CWE-794: Incomplete Filtering of Multiple Instances of Special Elements

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1[email protected]Secondary9.3CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
3.1CNADECLARED9.3CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Owasp Owasp Modsecurity Core Rule Set All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Coreruleset Coreruleset affected < 4.22.0 Not specified
CNA Coreruleset Coreruleset affected < 3.3.8 Not specified

References

ReferenceSourceLinkTags
github.com/daytriftnewgen/CVE-2026-21876 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/coreruleset/coreruleset/releases/tag/v3.3.8 [email protected] github.com Product, Release Notes
github.com/coreruleset/coreruleset/releases/tag/v4.22.0 [email protected] github.com Product, Release Notes
github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5 [email protected] github.com Exploit, Vendor Advisory
github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e... [email protected] github.com Patch
github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e... [email protected] github.com Patch
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