Affected: Homebrew: aider

``` ============================================================================ GIF seek keeps rejected size after DecompressionBombError, allowing DoS Location: src/PIL/GifImagePlugin.py:293 in GifImageFile._seek() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ```

A GIF of about 60 bytes can make Pillow allocate gigabytes of memory. This affects applications that catch the "image too large" error raised while stepping to a later animation frame and then keep using the same image object. Pillow correctly refuses the oversized frame, but it stores the refused dimensions on the image object anyway, and later operations size their memory from them. An attacker who can upload a GIF to such a service can exhaust its memory: the process either fails with an out-of-memory error after committing gigabytes, or is killed by the operating system. There is no memory corruption.

The bug is in `GifImageFile._seek()` (`src/PIL/GifImagePlugin.py:292-294`). When a frame's extent enlarges the image, the code assigns the new size to `self._size` and only then calls `Image._decompression_bomb_check()`. Nothing restores the old size when `DecompressionBombError` is raised, because `seek()` only rolls back on `EOFError`. After the caught error, `im.size` reports the rejected size while the pixel buffer `im.im` is still the 1×1 first frame. Because the extent is a 16-bit offset plus a 16-bit size, that rejected s…

Affected: python-pillow Pillow

Pillow is a Python imaging library. From 9.2.0 until 13.0.0, Pillow can retain a rejected GIF frame size after a decompression-bomb exception. In GifImageFile._seek, a crafted GIF can leave rejected dimensions stored after Image.DecompressionBombError; if an application catches that exception and continues processing the same image object, later seek or load operations allocate according to those dimensions and can exhaust memory, denying service. This issue is fixed in version 13.0.0.