libtiff's tiffcrop tool has a uint32_t underflow which leads to out of bounds read and write in the extractContigSamples8bits routine

libtiff's tiffcrop tool has a uint32_t underflow which leads to out of bounds read and write in the extractContigSamples8bits routine. An attacker who supplies a crafted file to tiffcrop could trigger this flaw, most likely by tricking a user into opening the crafted file with tiffcrop. Triggering this flaw could cause a crash or potentially further exploitation.