The Diffie-Hellman Key Agreement Protocol allows remote attackers (from the client side) to send arbitrary numbers that are actually not public keys, and trigger expensive server-side DHE modular-exponentiation calculations, aka a D(HE)at or D(HE)ater attack. The client needs very little CPU resources and network bandwidth. The attack may be more disruptive in cases where a client can require a server to select its largest supported key size. The basic attack scenario is that the client must claim that it can only communicate with DHE, and the server must be configured to allow DHE.
The L2TP implementation of MPD before 5.9 allows a remote attacker who can send specifically crafted L2TP control packet with AVP Q.931 Cause Code to execute arbitrary code or cause a denial of service (memory corruption).
The PPP implementation of MPD before 5.9 allows a remote attacker who can send specifically crafted PPP authentication message to cause the daemon to read beyond allocated memory buffer, which would result in a denial of service condition.