Affected: python-pillow Pillow

Pillow is a Python imaging library. From 5.2.0 until 12.3.0, Pillow's TGA RLE encoder reads past its packed row buffer when saving a mode 1 image with TGA RLE compression, allowing adjacent process heap bytes to be copied into the generated TGA file. This issue is fixed in version 12.3.0.

Affected: PyPI: Pillow

### 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:

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

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

`src/libIma…