CVE Tools
Sign in

CVE-2026-33691

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

Published: Apr 2, 2026Updated: Apr 18, 2026 Sources: CVE List NVDCWE-178
NVD MITRE
6.8CVSSMEDIUM
EPSS Score
0.9%
Top 46.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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 Vector Breakdown

AV:NAC:HPR:NUI:NS:CC:NI:HA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:CScope
Changed
Impact
C:NConfidentiality
None
I:HIntegrity
High
A:NAvailability
None
Open in CVSS calculator →

Weaknesses

CWE-178

Affected Products

owasp modsecurity core rule setowasp
Mixed
Networking Infrastructure / firewall
corerulesetcoreruleset
Mixed
Networking Infrastructure / firewall
owasposs-projectUSNetworking Infrastructureaka owasp modsecurity core rule set, modsecurity, modsecurity-crs
corerulesetoss-projectNetworking Infrastructureaka coreruleset (owasp modsecurity core rule set)

Exploitability

Official Patch Available
Workaround Available

References

https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02
github.com
https://github.com/coreruleset/coreruleset/pull/4546
github.com
https://github.com/coreruleset/coreruleset/pull/4547
github.com
and 7 more references View all →

Timeline

Published
Apr 2, 2026
Last Updated
Apr 18, 2026
News mentions
1

Unlock Complete Vulnerability Intelligence

Get the full picture for CVE-2026-33691 and every CVE in our database. Create a free account — no credit card required.

Create Free Account
Plain-language analysis
Impact assessment and exploitation scenario in plain English
Attack graph visualization
Interactive attack path and kill chain mapping
Exploit details & PoC links
ExploitDB, Metasploit, GitHub PoCs with direct links
Nuclei scanner templates
Ready-to-use vulnerability scanner templates
Full remediation guide
Patch instructions, workarounds, and compliance impact
Interactive AI chat
Ask questions about this vulnerability in natural language
Related vulnerabilities
Semantically similar CVEs and attack patterns
REST API & MCP access
Integrate vulnerability data into your workflows