CVE-2026-0859: TYPO3 CMS Allows Insecure Deserialization via Mailer File Spool

Problem

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.

References

• TYPO3-CORE-SA-2026-004