In Eclipse Californium version 2.0.0 to 2.6.4 and 3.0.0-M1 to 3.0.0-M3, the certificate based (x509 and RPK) DTLS handshakes accidentally succeeds without verifying the server side's signature on the client side, if that signature is not included in the server's ServerKeyExchange.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:HA:N7.5/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NOther