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BIT-pillow-2026-59199 — Pillow: Heap out-of-bounds write `Image.paste()` / `Image.crop()` via signed coordinate overflow

2026-10-01T11:33:13.735093+00:00

Affected: Bitnami: pillow

Pillow is a Python imaging library. Prior to 12.3.0, Pillow public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits in Image.paste(), Image.crop(), or Image.alpha_composite(). This issue is fixed in version 12.3.0.

CVE-2026-59199 — Pillow: Heap out-of-bounds write `Image.paste()` / `Image.crop()` via signed coordinate overflow

2026-10-01T11:33:13.735176+00:00

Affected: python-pillow Pillow

GHSA-6r8x-57c9-28j4 — Pillow: Heap out-of-bounds write `Image.paste()` / `Image.crop()` via signed coordinate overflow

2026-10-01T11:33:13.735220+00:00

Affected: PyPI: Pillow

### Summary

Pillow's public image coordinate APIs can trigger a native heap out-of-bounds write when given coordinates near the signed 32-bit integer limits. In 4-byte pixel modes such as `RGBA`, this becomes a controlled backward heap underwrite: for a source image of width `W`, Pillow writes `4 * W` attacker-controlled bytes starting `4 * W` bytes before the destination row pointer. With successful large image allocation, the theoretical upper bound is ~2 GiB backwards from the destination row.

Minimal public API trigger:

```python from PIL import Image

INT_MIN = -(1 << 31)

src = Image.new("RGBA", (2, 1), (0x41, 0x42, 0x43, 0x44)) dst = Image.new("RGBA", (8, 1)) dst.paste(src, ((1 << 31) - 2, 0, INT_MIN, 1)) ```

The same root cause is also reachable through `Image.crop()` and `Image.alpha_composite()`. No private API, ctypes, custom Python object, or malformed image file is needed.

This has been confirmed as an ASAN heap-buffer-overflow write. On normal non-ASAN Pillow builds, the minimal trigger corrupts the heap and aborts with `double free or corruption (out)`

### Details

`src/PIL/Image.py:paste()` accepts a 4-tuple box and passes it to the native `ImagingCore.paste()` method:

```python self.im.paste(source, box) ```

`src/_imaging.c:_paste()` parses the four Python coordinates into signed `int` values and calls `ImagingPaste()`:

```c int x0, y0, x1, y1; PyArg_ParseTuple(args, "O(iiii)|O!", &source, &x0, &y0, &x1, &y1, ...); status = ImagingPaste(self->image,…

PYSEC-2026-3451

2026-10-01T11:33:13.735322+00:00

Affected: PyPI: pillow