Affected: Homebrew: aider

``` ============================================================================ Memory disclosure and segfault in libtiff encoder via crafted TIFF tags Location: src/encode.c:1014 in PyImaging_LibTiffEncoderNew() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ```

A crafted TIFF file of a few hundred bytes makes Pillow copy an attacker-chosen amount of its own process memory into the TIFF it writes back out, or crash the process outright. The trigger is an ordinary `Image.open()` followed by a bare `im.save(fp, "TIFF")`. The only precondition is that the application re-saves images as TIFF. When the uploaded file is compressed, Pillow routes that save through libtiff automatically, with no options from the application. The attached reproducer does this with a 356-byte LZW TIFF: one crafted tag comes back holding 65536 bytes taken from `_imaging.so`'s read-only data, and a second crafted tag makes the worker die with SIGSEGV on every run.

The bug is in `PyImaging_LibTiffEncoderNew` (`src/encode.c`). It decides what arguments to pass to the variadic `TIFFSetField()` from the shape of the Python value (scalar, tuple or bytes). It assumes its `ImagingLibTiffMergeFieldInfo()` call defined how libtiff will read them. But `TIFFMergeFieldInfo()` never overrides libtiff's built-in field table, so libtiff reads the arguments according to its own definition of the tag:

- For a counted array tag such as…