P-Net before 1.0.3 does not validate the LengthPeerStationName field of a CheckPeers block in get_check_peer(). The received length (up to 255) was used to copy data into the 241-byte peer station name buffer and to place the terminating NUL byte, so a crafted block writes up to 15 bytes past the end of the buffer. This can lead to a crash (denial of service) or potentially arbitrary code execution. Requires establishment of session that needs ADJACENT network access.