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.