The parse_notify function in util.c in sgminer before 4.2.2 and cgminer 3.3.0 through 4.0.1 allows man-in-the-middle attackers to cause a denial of service (application exit) via a crafted (1) bbversion, (2) prev_hash, (3) nbit, or (4) ntime parameter in a mining.notify action stratum message.
