CVE-2026-33691
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 ).
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (3.58%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 3.58% probability · 89th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-178
- Affected
- owasp/owasp modsecurity core rule set
- Source
- security-advisories@github.com
References
- https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02Patch
- https://github.com/coreruleset/coreruleset/pull/4546Issue Tracking, Patch
- https://github.com/coreruleset/coreruleset/pull/4547Issue Tracking, Patch
- https://github.com/coreruleset/coreruleset/pull/4548Patch
- https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9Product, Release Notes
- https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0Product, Release Notes
- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2wMitigation, Patch, Vendor Advisory
- http://seclists.org/fulldisclosure/2026/Apr/0Mailing List, Third Party Advisory
- http://www.openwall.com/lists/oss-security/2026/03/29/2Mailing List, Third Party Advisory
- http://www.openwall.com/lists/oss-security/2026/04/18/4
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.