Improper Handling of Case Sensitivity Affecting mod_security_crs package, versions <0:4.2.0-1.amzn2023.0.3


Severity

Recommended
medium

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
3.58% (89th percentile)

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  • Snyk IDSNYK-AMZN2023-MODSECURITYCRS-16068046
  • published15 Apr 2026
  • disclosed2 Apr 2026

Introduced: 2 Apr 2026

CVE-2026-33691  (opens in a new tab)
CWE-178  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 mod_security_crs to version 0:4.2.0-1.amzn2023.0.3 or higher.
This issue was patched in ALAS2023-2026-1562.

NVD Description

Note: Versions mentioned in the description apply only to the upstream mod_security_crs package and not the mod_security_crs package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

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 Base Scores

version 3.1