OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks

MITRE NVD CVE.ORG Print: PDF PDF

Summary

CVECVE-2026-33691
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-02 16:16:22 UTC
Updated2026-04-02 16:16:22 UTC
DescriptionThe 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.

Risk And Classification

Primary CVSS: v3.1 6.8 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N

Problem Types: CWE-178 | CWE-178 CWE-178: Improper Handling of Case Sensitivity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
3.1CNADECLARED6.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Coreruleset Coreruleset affected < 3.3.9 Not specified
CNA Coreruleset Coreruleset affected >= 4.0.0-rc1, < 4.25.0 Not specified

References

ReferenceSourceLinkTags
github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w [email protected] github.com
www.openwall.com/lists/oss-security/2026/03/29/2 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com
github.com/coreruleset/coreruleset/pull/4546 [email protected] github.com
github.com/coreruleset/coreruleset/pull/4547 [email protected] github.com
github.com/coreruleset/coreruleset/releases/tag/v3.3.9 [email protected] github.com
github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a... [email protected] github.com
github.com/coreruleset/coreruleset/releases/tag/v4.25.0 [email protected] github.com
github.com/coreruleset/coreruleset/pull/4548 [email protected] github.com
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