A python script to see if images have residual data after cropping (CVE-2023-21036).

detect_bad_crop_simple.py

import sys

STANDARD_IEND = b'\x00\x00\x00\x00IEND\xae\x42\x60\x82'

# https://en.wikipedia.org/wiki/PNG
# https://en.wikipedia.org/wiki/ACropalypse
# https://github.com/infobyte/CVE-2023-21036

# USAGE:  detect_bad_crop_simple.py <png1> <png2> ...

if len(sys.argv) == 1:
    print(f"Usage: {sys.argv[0]} png_file1 png_file2 ...")
    
    # DEBUG:
    #sys.argv.append("./image.png")
    sys.exit(1)

for filename in sys.argv[1:]:
    try:
        with open(filename, "rb") as f:
            all_bytes = f.read()
            count = all_bytes.count(STANDARD_IEND)

            if count > 1:
                # Additional data found after footer likely.
                print(filename)
    except Exception as ex:
        print(f"{filename}: {ex}")