The png_err function in pngerror.c in libpng 1.0.x before 1.0.55, 1.2.x before 1.2.45, 1.4.x before 1.4.8, and 1.5.x before 1.5.4 makes a function call using a NULL pointer argument instead of an empty-string argument, which allows remote attackers to cause a denial of service (application crash) via a crafted PNG image.
The png_handle_sCAL function in pngrutil.c in libpng 1.0.x before 1.0.55, 1.2.x before 1.2.45, 1.4.x before 1.4.8, and 1.5.x before 1.5.4 does not properly handle invalid sCAL chunks, which allows remote attackers to cause a denial of service (memory corruption and application crash) or possibly have unspecified other impact via a crafted PNG image that triggers the reading of uninitialized memory.
pngrtran.c in libpng 1.5.x before 1.5.1 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted palette-based PNG image that triggers a buffer overflow, related to the png_do_expand_palette function, the png_do_rgb_to_gray function, and an integer underflow. NOTE: some of these details are obtained from third party information.