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CVE-2026-21876— OWASP CRS has multipart bypass using multiple content-type parts

Quick assessment

Affected
coreruleset coreruleset
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

OWASP CRS是CRS Project开源的一套攻击检测规则集。 OWASP CRS 4.22.0之前版本和3.3.8之前版本存在安全漏洞，该漏洞源于处理多部分请求时规则922110存在缺陷，可能导致恶意字符集被忽略。

CVSS 9.3 · Critical EPSS 17.51% · P97

Public Exploits 1

ExploitDB · 1 EDB-52558 [webapps]

Possible ATT&CK Techniques 1 AI

T1505.003 · Web Shell
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I. Basic Information for CVE-2026-21876

Vulnerability Information
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Vulnerability Title
OWASP CRS has multipart bypass using multiple content-type parts
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对特殊元素的多个实例的过滤不完全
Source: CVE Program / CVE List V5
Vulnerability Title
OWASP CRS 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
OWASP CRS是CRS Project开源的一套攻击检测规则集。 OWASP CRS 4.22.0之前版本和3.3.8之前版本存在安全漏洞，该漏洞源于处理多部分请求时规则922110存在缺陷，可能导致恶意字符集被忽略。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
coreruleset coreruleset < 4.22.0 -

II. Public POCs for CVE-2026-21876

# POC Description Source Link Shenlong Link
1 CVE-2026-21876 OWASP ModSecurity CRS WAF bypass (docker container + minimal PoC). https://github.com/daytriftnewgen/CVE-2026-21876 POC Details
AI-Generated POC Premium
Qwen3.6-35B-A3B · 9693 chars
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III. Intelligence Information for CVE-2026-21876

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Patches & Fixes for CVE-2026-21876 (1)

IV. Related Vulnerabilities

Same product: coreruleset
Same vendor: coreruleset
Same weakness: CWE-794

V. Comments for CVE-2026-21876

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