GHSA-pg7v-jwj7-p798: Pillow EpsImagePlugin negative %%BeginBinary byte count causes infinite loop denial of service

Summary Pillow's EPS parser (PIL/EpsImagePlugin.py) accepts a negative byte count in the %%BeginBinary directive. A crafted EPS file can cause Image.open() to seek backwards to the same directive and parse it repeatedly, resulting in an infinite loop and CPU denial of service. The issue is triggered during Image.open(), does not require Image.load(), and does not require Ghostscript execution. Confirmed affected versions: Pillow 12.0.0 through 12.2.0. Details The issue is in the EPS parser in PIL/EpsImagePlugin.py. When parsing an EPS %%BeginBinary directive, Pillow reads the byte count from the file and passes it directly to a relative seek operation without validating that the value is non-negative. Relevant code: elif bytes_mv[:14] == b"%%BeginBinary:": bytecount = int(byte_arr[14:bytes_read]) self.fp.seek(bytecount, os.SEEK_CUR) There is no validation that bytecount is non-negative. If an attacker provides a negative value such as %%BeginBinary:-18, the parser moves the file pointer backwards from the end of the directive line to the same line region. The next parser iteration reads the same %%BeginBinary:-18 directive again, performs the same backward seek, and repeats indefinitely. This causes Image.open() to hang in an infinite loop and consume CPU. In local testing, the issue is present in Pillow 12.0.0, 12.1.0, 12.1.1, and 12.2.0. Pillow 11.3.0 did not hang with the same PoC, so this appears to affect the 12.x EPS parsing path. PoC Save the following content as pillow_eps_beginbinary_dos.eps: %!PS-Adobe-3.0 EPSF-3.0 %%BoundingBox: 0 0 1 1 %%EndComments % dummy comment after transition %%BeginBinary:-18 %%EOF Then run: python -m pip install "Pillow==12.2.0" python - <<'PY' from PIL import Image Image.open("pillow_eps_beginbinary_dos.eps") PY Expected behavior: Pillow should reject the malformed EPS file with a parser exception. Actual behavior: the process does not return. It hangs inside Image.open() and continuously consumes CPU. The loo