In strongSwan before 5.9.5, a malicious responder can send an EAP-Success message too early without actually authenticating the client and (in the case of EAP methods with mutual authentication and EAP-only authentication for IKEv2) even without server authentication.

Affected: Ubuntu:18.04:LTS: strongswan, Ubuntu:20.04:LTS: strongswan

Zhuowei Zhang discovered that stringSwan incorrectly handled EAP authentication. A remote attacker could use this issue to cause strongSwan to crash, resulting in a denial of service, or possibly bypass client and server authentication.