CVE-2026-33691 Details
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.
A vulnerability exists in the OWASP Core Rule Set (CRS) versions prior to 3.3.9 and 4.25.0, allowing the upload of files with dangerous extensions such as .php, .phar, .jsp, and .jspx. This bypass is achieved by inserting whitespace padding in the filename, which the affected rules do not properly normalize before checking the file extension. As a result, the extension check fails to identify the file as potentially harmful. Exploitation of this vulnerability is most effective on Windows systems that trim whitespace from filenames before execution, but can also occur on Linux systems under certain conditions.
Users should upgrade to OWASP CRS versions 3.3.9, 4.25.0, or 4.8.x. Security fixes are backported to supported branches.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Apr 2, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| http://seclists.org/fulldisclosure/2026/Apr/0 | CVE | Mailing ListThird Party Advisory |
| http://www.openwall.com/lists/oss-security/2026/03/29/2 | CVE | Mailing ListThird Party Advisory |
| http://www.openwall.com/lists/oss-security/2026/04/18/4 | CVE | |
| https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02 | [email protected] | Patch |
| https://github.com/coreruleset/coreruleset/pull/4546 | [email protected] | Issue TrackingPatch |
| https://github.com/coreruleset/coreruleset/pull/4547 | [email protected] | Issue TrackingPatch |
| https://github.com/coreruleset/coreruleset/pull/4548 | [email protected] | Patch |
| https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9 | [email protected] | ProductRelease Notes |
| https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0 | [email protected] | ProductRelease Notes |
| https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w | [email protected] | MitigationPatchVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-178 | Improper Handling of Case Sensitivity | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| owasp owasp modsecurity core rule set | < 3.3.9 >= 4.0.0, < 4.25.0 |
CPE
Remediation
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Change History
8 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 24, 2026 | CVE Translated | [email protected] |
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Apr 18, 2026 | CVE Modified | CVE |
| Apr 7, 2026 | Initial Analysis | [email protected] |
| Apr 3, 2026 | CVE Modified | CVE |
| Apr 2, 2026 | New CVE Received | [email protected] |
| Apr 2, 2026 | CVE Modified | CVE |