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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Owasp | Owasp Modsecurity Core Rule Set | < 3.3.9 |
Related Weaknesses (CWE)
References
- https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79aPatch
- https://github.com/coreruleset/coreruleset/pull/4546Issue TrackingPatch
- https://github.com/coreruleset/coreruleset/pull/4547Issue TrackingPatch
- https://github.com/coreruleset/coreruleset/pull/4548Patch
- https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9ProductRelease Notes
- https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0ProductRelease Notes
- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gvMitigationPatchVendor Advisory
- http://seclists.org/fulldisclosure/2026/Apr/0Mailing ListThird Party Advisory
- http://www.openwall.com/lists/oss-security/2026/03/29/2Mailing ListThird Party Advisory
- http://www.openwall.com/lists/oss-security/2026/04/18/4
FAQ
What is CVE-2026-33691?
CVE-2026-33691 is a vulnerability with a CVSS score of 6.8 (MEDIUM). 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 tha...
How severe is CVE-2026-33691?
CVE-2026-33691 has been rated MEDIUM with a CVSS base score of 6.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-33691?
Check the references section above for vendor advisories and patch information. Affected products include: Owasp Owasp Modsecurity Core Rule Set.