Integer underflow in Ettercap 0.8.1 allows remote attackers to cause a denial of service (out-of-bounds write) and possibly execute arbitrary code via a small (1) size variable value in the dissector_dhcp function in dissectors/ec_dhcp.c, (2) length value to the dissector_gg function in dissectors/ec_gg.c, or (3) string length to the get_decode_len function in ec_utils.c or a request without a (4) username or (5) password to the dissector_TN3270 function in dissectors/ec_TN3270.c.