What’s Vulnerable › Vulnerabilities

CVE-2026-96637: Pillow: Decompression bomb check bypass in SpiderImagePlugin.seek() leads to unbounded allocation DoS

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-21 · updated 2026-10-27
• Weakness: CWE-400

Description

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.

Affected products

• python-pillow Pillow: before 13.0.0 — fixed in 13.0.0
• Pypi Pillow: before 13.0.0; 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 (+101) — fixed in 13.0.0
• python-pillow Pillow: before 13.0.0

How to fix

Upgrade to a fixed version: python-pillow Pillow 13.0.0; Pypi Pillow 13.0.0. Check the vendor advisory for mitigations.

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

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