TYPO3-CORE-SA-2026-004: Insecure Deserialization via Mailer File Spool

• Component Type: TYPO3 CMS
• Subcomponent: Mailer (ext:core)
• Release Date: January 13, 2026
• Vulnerability Type: Insecure Deserialization
• Affected Versions: 10.0.0-10.4.54, 11.0.0-11.5.48, 12.0.0-12.4.40, 13.0.0-13.4.22, 14.0.0-14.0.1
• Severity: Medium
• Suggested CVSS: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:H/SI:H/SA:H
• References: CVE-2026-0859, CWE-502

Problem Description

Local platform users who can write to TYPO3’s mail‑file spool directory can craft a file that the system will automatically deserialize without any class restrictions. This flaw allows an attacker to inject and execute arbitrary PHP code in the public scope of the web server.

The vulnerability is triggered when TYPO3 is configured with $GLOBALS['TYPO3_CONF_VARS']['MAIL']['transport_spool_type'] = 'file'; and a scheduler task or cron job runs the command mailer:spool:send. The spool‑send operation performs the insecure deserialization that is at the core of this issue.

Solution

Update to TYPO3 versions 10.4.55 ELTS, 11.5.49 ELTS, 12.4.41 LTS, 13.4.23 LTS, 14.0.2 that fix the problem described.

Credits

Thanks to Vitaly Simonovich for reporting this issue, and to TYPO3 security team members Elias Häußler and Oliver Hader for fixing it.

General Advice

Follow the recommendations that are given in the TYPO3 Security Guide. Please subscribe to the typo3-announce mailing list.

General Note

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