Redaxo has a Mediapool isAllowedExtension bypass via multi-segment filename that leads to authenticated RCE on Apache mod_php multi-extension handlers

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2026-53599: 0.51% estimated exploitation activity in the next 30 days; percentile 43.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary rexmediapool::isAllowedExtension in redaxo/src/addons/mediapool/lib/mediapool.php accepts filenames that contain a blocked extension as a non-terminal segment of a longer extension chain, for example shell.php.any.jpg. The check only catches the blocked extension when it appears at the end of the filename or immediately before the final extension. An authenticated backend user with mediapool upload permission can upload a JPEG/PHP polyglot named shell.php.any.jpg and, on web servers whose PHP handler matches .php as any segment (modmime AddHandler-style, or any FilesMatch regex without an end anchor), request the file from the public media/ directory to execute arbitrary PHP as the web-server user. The vulnerable check is a regression introduced in commit 9d008697d (PR #6213, Feb 7 2025), which weakened a previously correct strcontains check into a pair of strendswith checks. The earlier check, in place since 2018 specifically to defend against double-extension attacks, would…

Published by the source

31 Jul 2026, 19:43 UTC

Last modified by the source

31 Jul 2026, 20:11 UTC

Source last checked

26 Oct 2026, 14:50 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-98pp-vccm-qm25

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-98pp-vccm-qm25

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# Patch Next advisory brief: CVE-2026-53599

Advisory: Redaxo has a Mediapool isAllowedExtension bypass via multi-segment filename that leads to authenticated RCE on Apache mod_php multi-extension handlers
IDs: CVE-2026-53599, GHSA-98pp-vccm-qm25
Record: https://patchnext.com/advisories/cve-2026-53599 (revision 2, source checked 26 Oct 2026, 14:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: redaxo/source 5.21.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist redaxo/source: affected >= 5.18.2, < 5.21.1; fixed in 5.21.1

## Suggested inspection (read-only)
- Packagist redaxo/source: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on redaxo/source.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-98pp-vccm-qm25 (OSV record GHSA-98pp-vccm-qm25 lists affected ranges: Packagist redaxo/source >=5.18.2 <5.21.1 (fixed))
- Verified: https://github.com/advisories/GHSA-98pp-vccm-qm25 (GitHub-reviewed advisory GHSA-98pp-vccm-qm25 lists affected ranges: Packagist redaxo/source >=5.18.2 <5.21.1)

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