The npb_protocol_error function in sna V5router64 in IBM Communications Server for Windows 6.1.3 and Communications Server for AIX (aka CSAIX or CS/AIX) in sna.rte before 6.3.1.2 allows remote attackers to cause a denial of service (daemon crash) via APPC data containing a GDSID variable with a GDS length that is too small.