MEDIUM CWE-178
CVE-2026-33691
OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks
6.8/ 10
CVSS 3.1
Medium severity
3.8%
EPSS exploit odds
Chance of exploitation in the next 30 days
Higher than 90% of all CVEs
Not listed
CISA KEV catalog
No confirmed in-the-wild exploitation on CISA's list.
Timeline
- Published
- Apr 2, 2026
- Updated
- Apr 18, 2026
- First covered
- Aug 10, 2026
- Latest story
- 3 months ago
Summary
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.
CWE-178Improper Handling of Case Sensitivity
Attack profile
Attack vectorNetwork
ComplexityHigh
PrivilegesNone
User interactionNone
ScopeChanged
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:NAffected products
- coreruleset< 3.3.9>= 4.0.0-rc1, < 4.25.0