An unauthenticated attacker can exploit the Frontend 'validate' action to blindly instantiate arbitrary PHP classes. The impact depends on environment setup but appears limited at this time.
Exploitability
AV:NAC:LAT:NPR:NUI:NVulnerable System
VC:NVI:NVA:LSubsequent System
SC:NSI:NSA:N6.9/CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:NOther