CVE-2026-33691 — The OWASP core rule set (CRS) is a set of generic attack detection rules for use

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

01What is this vulnerability?

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…

02Affected products

No structured affected-product list available — see references below for vendor advisories.

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:

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07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2026-04-02T16:16:22.593
• Last modified: 2026-07-24T21:10:00.143

09References

• github.com — https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a…
• github.com — https://github.com/coreruleset/coreruleset/pull/4546
• github.com — https://github.com/coreruleset/coreruleset/pull/4547
• github.com — https://github.com/coreruleset/coreruleset/pull/4548
• github.com — https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9
• github.com — https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0
• github.com — https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv…
• seclists.org — http://seclists.org/fulldisclosure/2026/Apr/0
• www.openwall.com — http://www.openwall.com/lists/oss-security/2026/03/29/2
• www.openwall.com — http://www.openwall.com/lists/oss-security/2026/04/18/4