I attach the patch to fix that bug
--- ettercap-0.7.3.orig/src/protocols/ec_tcp.c +++ ettercap-0.7.3/src/protocols/ec_tcp.c @@ -116,7 +116,7 @@ tcp = (struct tcp_header *)DECODE_DATA; opt_start = (u_char *)(tcp + 1); - opt_end = (u_char *)((int)tcp + tcp->off * 4); + opt_end = (u_char *)(tcp + tcp->off * 4); DECODED_LEN = (u_int32)(tcp->off * 4);