Multiple off-by-one errors in libpng before 1.2.32beta01, and 1.4 before 1.4.0beta34, allow context-dependent attackers to cause a denial of service (crash) or have unspecified other impact via a PNG image with crafted zTXt chunks, related to (1) the png_push_read_zTXt function in pngread.c, and possibly related to (2) pngtest.c.