CVE-2026-33691 MEDIUM

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

Vendor Coreruleset
Product coreruleset
Weakness CWE-178
Published April 2, 2026
Last update April 18, 2026

CVSS base score

6.8/10
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Confidentiality None
Integrity High

CVSS vector

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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

April 2, 2026 CVE published
April 18, 2026 Record updated