CVE-2026-21876

CVE Enrichment

CVSS: 5.3 MEDIUM
EPSS: 17.75%
EPSS Percentile: 97.17%
CISA KEV: Not listed

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.

Technical Details

CVSS Version: 3.1
CNA / NVD Source: [email protected]
Published: 08-Jan-2026 21:15
Last Modified: 17-Jun-2026 17:19
EPSS Date: 2026-11-04
CWE: CWE-794

CVSS Vector


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

CNA Products / Version Status

coreruleset · coreruleset Source: CNA · [email protected]
Default status: unknown

< 4.22.0 — affected
< 3.3.8 — affected

Affected Products / Versions

owasp / owasp_modsecurity_core_rule_set Source: NVD CPE · affected
Version / affected range: * · before (exclusive) 3.3.8
cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set:*:*:*:*:*:*:*:*
owasp / owasp_modsecurity_core_rule_set Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 4.0.0 · before (exclusive) 4.22.0
cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set:*:*:*:*:*:*:*:*

References

Last enrichment sync: 05-Nov-2026 06:43
Sources: NVD · FIRST EPSS · CISA KEV
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Reported Context (1)

Progress Software fixes sneaky WAF bypass vulnerability (CVE-2026-21876) Week in Review: Claude Mythos Finds 271 Firefox Vulnerabilities; Vercel Reports Breach

CVE (2)

Malware (3)

People (3)

Threat Actors (3)

MITRE ATT&CK (4)

Vendors (7)

Products (11)

Tools (7)

Industries (2)

Countries (5)

Note: Related entities, including threat actors, malware, CVEs, MITRE ATT&CK techniques, vendors, products, tools, countries, and industries, are shown when they appear in the same reporting. Their presence does not necessarily mean they were targeted, compromised, vulnerable, responsible for the activity, or directly involved in the incident.