P-Net before 1.0.3 does not validate the length of a received Ethernet frame in pf_eth_recv() before reading the EtherType, any VLAN tags and the PROFINET FrameID. The VLAN tag loop had no upper bound, so a truncated frame, or a frame consisting only of VLAN tags, makes the function read past the end of the receive buffer. This can cause a crash (denial of service) or disclose memory content.