CVE-2026-33691: Owasp Modsecurity Core Rule Set

High severity, CVSS 7.5. EPSS: 1.6% chance of exploitation in the next 30 days.

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.

Affected products

• Owasp Owasp Modsecurity Core Rule Set: before 3.3.9 (fixed in 3.3.9); from 4.0.0, before 4.25.0 (fixed in 4.25.0)

Published 2026-04-02. Last modified 2026-07-24.