Executive brief
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.
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
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