P-Net before 1.0.3 passes the application alarm callback a data length derived from the variable part length field of a received RTA alarm frame without checking it against the length of the received frame. A short frame can make the callback receive a length of up to 65507 bytes. An application that copies the reported number of bytes reads past the end of the receive buffer. The attacker must have established an Application Relationship and requires ADJACENT network access. Applications that do not use the alarm data are not affected.