TI-2026-17577 Aliases CVE-2026-21876

OWASP CRS has multipart bypass using multiple content-type parts

MEDIUM 63CWE-794Published 2026-01-08 · Updated 2026-04-09

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: High · Low · None
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.1735 97th percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Fixed coreruleset (coreruleset): 4.22.0, 3.3.8

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
coreruleset	coreruleset	before 4.22.0; before 3.3.8	4.22.0, 3.3.8	Patch available	CNA

coreruleset Vendorcoreruleset Affected before 4.22.0; before 3.3.8 Fixed in 4.22.0, 3.3.8 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set::::::::	before 3.3.8; 4.0.0 to before 4.22.0	Vulnerable	owasp-modsecurity

cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set:*:*:*:*:*:*:*:* Versions before 3.3.8; 4.0.0 to before 4.22.0 Vulnerable ·owasp-modsecurity

Remediation

Fix · CNA coreruleset (coreruleset) Fixed in 4.22.0, 3.3.8

Timeline

2026-10-02 Threatist record created from CVE-2026-21876

References

Exploit 1

https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5

Patch 2

Other 2

TI-2022-18921 Partial rule set bypass in OWASP ModSecurity Core Rule Set by submitting a specially crafted HTTP Content-Type header CVSS 3.1CRITICAL 9.8
TI-2022-18922 Incorrect authorization in owasp-modsecurity ModSecurity Core Rule Set CVSS 3.1CRITICAL 9.8
TI-2021-14182 OWASP ModSecurity Core Rule Set 3.1.x before 3.1.2, 3.2.x before 3.2.1, and 3.3.x before… CVSS 3.1CRITICAL 9.8
TI-2020-14375 Modsecurity owasp-modsecurity-crs 3.2.0 (Paranoia level at PL1) has a SQL injection… CVSS 3.1CRITICAL 9.8
TI-2022-18924 Incorrect authorization in owasp-modsecurity ModSecurity Core Rule Set CVSS 3.1HIGH 7.5
TI-2022-18923 Response body bypass in OWASP ModSecurity Core Rule Set via a specialy crafted charset in the HTTP Accept header CVSS 3.1HIGH 7.5

See all 8 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences