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Fencer Vulns
medium 6.8

CVE-2026-33691 json

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

published 2026-04-02 7 mo ago modified 2026-07-24 3 mo ago also EUVD-2026-18352

cvss
6.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
3.8%
EPSS 3.8% chance of exploitation in 30 days, percentile 90%
public exploits
0
none known

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.

Patch / fix

  • owasp coreruleset 3.3.9, 4.25.0
  • owasp owasp_modsecurity_core_rule_set 3.3.9, 4.25.0
  • modsecurity-crs Debian 12 3.3.4-1+deb12u3
  • modsecurity-crs Debian 13 3.3.7-1+deb13u2
  • modsecurity-crs Debian 14 3.3.9-1

debian advisories DEBIAN-CVE-2026-33691

  • owasp-modsecurity-crs openSUSE Tumbleweed 4.29.0-1.1

opensuse advisories openSUSE-SU-2026:11632-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33691 updated cvss 6.8

coreruleset: OWASP Core Rule Set: File upload bypass via whitespace padding in filenames

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

3.84% chance of exploitation in the next 30 days, higher than 90% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

  • coreruleset coreruleset

Classification

Weakness
  • CWE-178 Improper Handling of Case Sensitivity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.