CVE-2026-42311: Pillow: OOB Write with Invalid PSD Tile Extents (Integer Overflow)

### Impact Processing a malicious PSD file could lead to memory corruption, potentially resulting in a crash or arbitrary code execution. ### Patches Patched version: 12.2.0 Pillow 12.1.1 addressed CVE-2026-25990 by adding checks for tile extents in PSD image decoding/encoding to prevent an out-of-bounds write. However, the bounds checks computed tile extent sums using types susceptible to integer overflow, meaning a PSD image with carefully chosen tile dimensions could produce values that wrap around and bypass the checks, still triggering an out-of-bounds write in src/decode.c and src/encode.c. The fix avoids adding extents together before comparison. ### Workarounds Use any version but affected versions: >= 10.3.0, < 12.2.0 ### Resources - Fix: https://github.com/python-pillow/Pillow/pull/9520 - Original issue: CVE-2026-25990 (Pillow 12.1.1)