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 dissectordhcp function in dissectors/ecdhcp.c, (2) length value to the dissectorgg function in dissectors/ecgg.c, or (3) string length to the getdecodelen function in ecutils.c or a request without a (4) username or (5) password to the dissectorTN3270 function in dissectors/ec_TN3270.c.