By exploiting the defVals parameter, attackers could bypass field‑level access checks during record creation in the TYPO3 backend. This gave them the ability to insert arbitrary data into prohibited exclude fields of a database table for which the user already has write permission for a reduced set of fields.
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.
Thanks to Daniel Windloff for reporting this issue, and to TYPO3 core & security team member Benjamin Franzke for fixing it.
10.4.5511.5.4912.4.4113.4.2314.0.2Exploitability
AV:NAC:LAT:NPR:LUI:NVulnerable System
VC:NVI:LVA:NSubsequent System
SC:LSI:LSA:L5.3/CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L