BIT-pillow-2026-96637

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BIT-pillow-2026-96637

Summary: Pillow: Decompression bomb check bypass in SpiderImagePlugin.seek() leads to unbounded allocation DoS

Details: Pillow is a Python imaging library. Prior to 13.0.0, SpiderImageFile.seek() in src/PIL/SpiderImagePlugin.py reparses a later SPIDER stack frame and replaces self._size without rerunning Image._decompression_bomb_check(). A tiny file can use a safe first frame to pass Image.open() and then declare very large dimensions in a later mode F frame. Loading that frame allocates approximately four bytes per attacker-declared pixel and can consume multiple gigabytes of memory. This issue is fixed in version 13.0.0.

References: https://github.com/python-pillow/Pillow/commit/7cb0e02389d8aac2a60896a490f572db0b07b841, https://github.com/python-pillow/Pillow/pull/10076, https://github.com/python-pillow/Pillow/releases/tag/13.0.0, https://github.com/python-pillow/Pillow/security/advisories/GHSA-g842-9rc4-69pw, https://nvd.nist.gov/vuln/detail/CVE-2026-96637