CVE-2026-53599 Redaxo has a Mediapool isAllowedExtension bypass via multi-segment filename that leads to authenticated RCE on Apache mod_php multi-extension handlers
Authenticated users can upload malicious files with multi-segment names to achieve remote code execution on servers with specific PHP handler configurations.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53599?
CVE-2026-53599 is a high-severity vulnerability in redaxo core, published on 31 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
REDAXO is a PHP-based content management system. From 5.18.2 until 5.21.1, rex_mediapool::isAllowedExtension in redaxo/src/addons/mediapool/lib/mediapool.php lets an authenticated backend user with media[upload] permission upload a JPEG/PHP polyglot named shell.php.any.jpg, which web servers with multi-extension PHP handlers can execute as the web-server user. This issue is fixed in version 5.21.1.
Weakness: CWE-434
Which versions are affected by CVE-2026-53599?
2 open source packages ship an affected version, including redaxo/source.
| Package | Affected | Fixed in |
|---|---|---|
redaxo/source Packagist | From 5.18.2 | 5.21.1 |
redaxo/source Packagist | From 5.18.2 | 5.21.1 |
How do I fix CVE-2026-53599?
Upgrade redaxo/source to 5.21.1 or later.
Is CVE-2026-53599 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53599 exists.
Sources
Also known as GHSA-98pp-vccm-qm25.