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CVE-2026-53599 high CVSS 7.5

Unrestricted File Upload in redaxo/source (CVE-2026-53599)

Summary

Vulnerability in redaxo/source (CVE-2026-53599). Successful exploitation can lead to full system takeover. Exploitable via shell.php.any.jpg. Mitigation: upgrade to 5.21.1 or later.

Original description

The description as published by the source.

Summary

rex_mediapool::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 (mod_mime 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 str_contains check into a pair of str_ends_with checks. The earlier check, in place since 2018 specifically to defend against double-extension attacks, would have blocked this payload.

The regression has shipped in every release from 5.18.2 through 5.21.0.

Details

Root cause

At the audited commit 6e0de42, isAllowedExtension performs three checks against the blocked-extension list:

// redaxo/src/addons/mediapool/lib/mediapool.php (104–130) @ 6e0de42
public static function isAllowedExtension(string $filename, ar…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-53599 has been found in redaxo/source.
Attackers can target a specific entry point like shell.php.any.jpg over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 7.5/10.
What to do: upgrade redaxo/source to 5.21.1 or later.
If unsure, ask your IT team or search "redaxo/source CVE-2026-53599" on the vendor's site.

CVE-2026-53599 (redaxo/source) — CWE-434 / CVSS v3 7.5
Attack vector: remote (network-reachable) / no user interaction
Attack surface: shell.php.any.jpg / AddHandler / FilesMatch / str_contains
Patched: 5.21.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-434) exists in redaxo/source. Attackers reach the vulnerable code path via shell.php.any.jpg.

📍 Affected scope

Check the vendor advisory for the affected versions of redaxo/source. Attack surface: shell.php.any.jpg / AddHandler / FilesMatch / str_contains.

🔥 Severity

Severity: High (CVSS 7.5/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 5.21.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'redaxo/source' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'redaxo/source' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で redaxo/source を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade redaxo/source to 5.21.1

    ステージング環境で 5.21.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

composer redaxo/source
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.21.1"}]}]
Packagist redaxo/source
[{"type":"ECOSYSTEM","events":[{"introduced":"5.18.2"},{"fixed":"5.21.1"}]}]

References

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