Multiple stack-based buffer overflows in the HMI application in DATAC RealFlex RealWin 2.1 (Build 6.1.10.10) and earlier allow remote attackers to execute arbitrary code via (1) a long username in an On_FC_CONNECT_FCS_LOGIN packet, and crafted (2) On_FC_CTAGLIST_FCS_CADDTAG, (3) On_FC_CTAGLIST_FCS_CDELTAG, (4) On_FC_CTAGLIST_FCS_ADDTAGMS, (5) On_FC_RFUSER_FCS_LOGIN, (6) unspecified "On_FC_BINFILE_FCS_*FILE", (7) On_FC_CGETTAG_FCS_GETTELEMETRY, (8) On_FC_CGETTAG_FCS_GETCHANNELTELEMETRY, (9) On_FC_CGETTAG_FCS_SETTELEMETRY, (10) On_FC_CGETTAG_FCS_SETCHANNELTELEMETRY, and (11) On_FC_SCRIPT_FCS_STARTPROG packets to port 910.