Certain chunk handlers in libpng before 1.0.29 and 1.2.x before 1.2.21 allow remote attackers to cause a denial of service (crash) via crafted (1) pCAL (png_handle_pCAL), (2) sCAL (png_handle_sCAL), (3) tEXt (png_push_read_tEXt), (4) iTXt (png_handle_iTXt), and (5) ztXT (png_handle_ztXt) chunking in PNG images, which trigger out-of-bounds read operations.