CVE-2026-53599: REDAXO CMS authenticated RCE via multi-extension upload bypass

CVE-2026-53599 · Severity: high · CVSS 7.5 · Published 2026-07-31

Redaxo, a content management system, contains a vulnerability in its media management component that allows authorized users to bypass file upload restrictions. By using specially crafted filenames with multiple extensions, an attacker can upload malicious scripts disguised as images. If the web server is configured to process these multi-extension files, the attacker can execute arbitrary code, potentially leading to a full takeover of the website and access to sensitive data.

Technologies: redaxo/source (Packagist), REDAXO. Vendors: Packagist, REDAXO.

Quick answers

Is CVE-2026-53599 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-53599 being exploited in the wild.
How severe is CVE-2026-53599?
High severity, with a CVSS score of 7.5, published 31 July 2026.
Which products and versions are affected?
redaxo/source (Packagist) >= 5.18.2, < 5.21.1, ECOSYSTEM:introduced=5.18.2,fixed=5.21.1; REDAXO >= 5.18.2, < 5.21.1; REDAXO CMS 5.18.2 to 5.21.0.
Is there a fix for CVE-2026-53599?
Yes. redaxo/source (Packagist): upgrade to 5.21.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-53599 attacked?
It is attacked over the network, in a web application.
Am I affected by CVE-2026-53599?
Check whether you run redaxo/source (Packagist), REDAXO or REDAXO CMS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • redaxo/source (Packagist): upgrade to 5.21.1 or later
    composer require redaxo/source:^5.21.1

Technical details

A regression in rex_mediapool::isAllowedExtension in Redaxo core (introduced in version 5.18.2) weakened filename validation by replacing a substring check with insufficient suffix checks. The current logic only blocks restricted extensions (like .php) if they appear at the very end of the filename or immediately before the final extension (e.g., .php.jpg). An authenticated attacker with media upload permissions can bypass this by using three or more segments (e.g., shell.php.any.jpg). On Apache servers using mod_mime AddHandler or non-anchored FilesMatch regex for PHP processing, the server will execute the PHP code embedded within the uploaded file. The issue is fixed in version 5.21.1.

Affected products

  • redaxo core >= 5.18.2, < 5.21.1

Identifiers

  • CVE-2026-53599
  • GHSA-98pp-vccm-qm25

Timeline

  • 2025-02-07: other: Vulnerability introduced via regression in commit 9d008697d
  • 2026-06-09: advisory: GitHub Advisory published
  • 2026-07-31: disclosed: CVE-2026-53599 published

References

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