CVE-2026-104890 Kunstmaan CMS: MediaBundle extension blacklist bypass allows authenticated administrators to upload executable PHP files leading to remote code execution
Authenticated administrators can bypass file extension blacklists to upload executable PHP files, resulting in remote code execution.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-104890?
CVE-2026-104890 is a high-severity vulnerability in KunstmaanBundlesCMS, published on 5 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
Kunstmaan CMS is an open source content management system based on the Symfony framework. Prior to 7.3.2, src/Kunstmaan/MediaBundle/Helper/File/FileHandler.php performs the blacklisted_extensions check case-sensitively in FileHandler::getFilePath and lowercases the stored extension afterward. An authenticated backend user with media access can upload a mixed-case executable extension such as PHP that bypasses the check and is stored in the web-accessible media directory with an executable lowercase extension. The default blacklist also omits several server-executable extension types, allowing the same code-execution impact where the web server executes uploaded files. This issue is fixed in version 7.3.2.
Weakness: CWE-434
Which versions are affected by CVE-2026-104890?
4 open source packages ship an affected version, including kunstmaan/bundles-cms and kunstmaan/media-bundle.
| Package | Affected | Fixed in |
|---|---|---|
kunstmaan/bundles-cms Packagist | All versions | 7.3.2 |
kunstmaan/bundles-cms Packagist | All versions | 7.3.2 |
kunstmaan/media-bundle Packagist | All versions | 7.3.2 |
kunstmaan/media-bundle Packagist | All versions | 7.3.2 |
How do I fix CVE-2026-104890?
Upgrade kunstmaan/bundles-cms to 7.3.2 or later.
Is CVE-2026-104890 being exploited?
There is no known exploitation of CVE-2026-104890 in the wild and no public exploit code.
Sources
Also known as GHSA-p279-5wcv-45vq.