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CVE-2026-33691— OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks

Quick assessment

Affected
coreruleset coreruleset
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
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 3.3.9之前版本和4.25.0之前版本存在安全漏洞，该漏洞源于文件扩展名检查未规范化空格，可能导致绕过文件上传限制。

CVSS 6.8 · Medium EPSS 1.58% · P75

Possible ATT&CK Techniques 1 AI

T1505.003 · Web Shell
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I. Basic Information for CVE-2026-33691

Vulnerability Information
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Vulnerability Title
OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks
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 3.3.9 and 4.25.0, a bypass was identified in OWASP CRS that allows uploading files with dangerous extensions (.php, .phar, .jsp, .jspx) by inserting whitespace padding in the filename (e.g. photo. php or shell.jsp ). The affected rules do not normalize whitespace before evaluating the file extension regex, so the dot-extension check fails to match. This issue has been patched in versions 3.3.9 and 4.25.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
大小写敏感处理不恰当
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 3.3.9之前版本和4.25.0之前版本存在安全漏洞，该漏洞源于文件扩展名检查未规范化空格，可能导致绕过文件上传限制。
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)

Affected Products

Vendor Product Affected Versions CPE Subscribe
coreruleset coreruleset < 3.3.9 -

II. Public POCs for CVE-2026-33691

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III. Intelligence Information for CVE-2026-33691

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Patches & Fixes for CVE-2026-33691 (4)

Vendor Advisories for CVE-2026-33691 (1)

Vendor Pages for CVE-2026-33691 (2)

IV. Related Vulnerabilities

Same product: coreruleset
Same vendor: coreruleset
Same weakness: CWE-178

V. Comments for CVE-2026-33691

Anonymous User
2026-05-15 18:10:45

<h1>Some distros still not patched</h1>

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