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Owasp Modsecurity Core Rule Set CVE-2026-21876

CRITICAL
Incomplete Filtering of Multiple Instances of Special Elements (CWE-794)
2026-01-08 security-advisories@github.com
Information Disclosure Owasp Modsecurity Core Rule Set
9.3
CVSS 3.1 · GitHub Advisory
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Severity by source

GitHub Advisory PRIMARY
9.3 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
None

Lifecycle Timeline

4
PoC Detected
Apr 09, 2026 - 16:16 vuln.today
Public exploit code
Patch released
Apr 09, 2026 - 16:16 nvd
Patch available
Analysis Generated
Mar 12, 2026 - 21:54 vuln.today
CVE Published
Jan 08, 2026 - 14:15 nvd
CRITICAL 9.3

DescriptionGitHub Advisory

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.

AnalysisAI

OWASP Core Rule Set (CRS) before 4.22.0 and 3.3.8 has a bug in rule 922110 that allows WAF bypass on multipart requests. The rule's capture variables get overwritten when processing multiple parts, allowing SQL injection and other attacks to slip through. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Craft multipart request with multiple parts
Delivery
Place malicious charset in early part
Exploit
Include legitimate charset in final part
Execution
Bypass rule 922110 detection
Impact
Execute injected attack payload
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Vulnerability AssessmentAI

Exploitation OWASP CRS versions prior to 4.22.0 (v4.x) or 3.3.8 (v3.x) deployed with web application firewall; multipart/form-data requests enabled; rule 922110 active in WAF ruleset. Additional conditions and limiting factors are described in the full assessment.
Risk Assessment CVSS 9.3 (Critical). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker crafts a multipart HTTP request with the SQL injection payload split across multiple parts. The CRS rule processes each part but overwrites its detection variables, allowing the combined payload to reach the backend application unfiltered.
Remediation Update CRS to 4.22.0 or 3.3.8. … Detailed patch versions, workarounds, and compensating controls in full report.
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Within 24 hours: Identify all affected systems and apply vendor patches immediately. …

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CVE-2026-21876 vulnerability details – vuln.today
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