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The vulnerability stems from the mailqueue extension’s incorporation of TYPO3’s FileSpool component code, which was previously patched in the core for insecure deserialization via TYPO3-CORE-SA-2026-004. The extension overwrites this core fix with its own implementation that lacks proper validation during deserialization. Specifically, when handling queued email data stored as serialized PHP objects, the extension’s FileSpool component fails to sanitize or validate input before deserializing it. This allows attackers to inject malicious serialized payloads into the queue system, which are then processed by the application. Upon deserialization, these payloads can trigger arbitrary object instantiation and code execution due to PHP’s deserialization mechanisms. The vulnerable code path exists in the extension’s methods responsible for reading and processing spooled files, typically accessed through administrative or web interfaces that manage mail queues. Even with a patched TYPO3 core, the extension reintroduces the flaw because it directly uses the extracted vulnerable code without the security checks. Exploitation requires access to the queue handling functionality, often via backend modules or APIs, where crafted serialized data can be submitted. This leads to full remote code execution on the server, compromising the system and potentially exposing sensitive data. The issue is resolved in the extension versions that reapply the core’s validation logic.
Platform: TYPO3 mailqueue extension
Version: <0.4.3, 0.5.0-0.5.1
Vulnerability: Insecure Deserialization
Severity: Critical
Date: 2026-01-20
Prediction: Patch released 2026-01-20
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`composer show typo3/mailqueue`
`grep -r “FileSpool” /path/to/typo3-ext/`
`php -r ‘echo serialize([“malicious” => “payload”]);’`
How Exploit:
Craft serialized payloads.
Inject via queue endpoints.
Execute arbitrary code.
Protection from this CVE
Update to 0.4.3/0.5.1.
Apply core patches.
Validate input data.
Impact:
Remote code execution.
System compromise.
Data breach.
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Sources:
Reported By: github.com
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