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Vulnerability · Published Oct 21, 2026 · Assigned by GitHub_M

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

High 7.1

In plain English

A high-severity uncontrolled resource consumption in Pillow from python-pillow. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 31% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)7.1High
Exploit odds (30 days)0.4%top 68.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12pillowno fix listedDEBIAN-CVE-2026-96637
Debian:13pillowno fix listedDEBIAN-CVE-2026-96637
Debian:14pillowno fix listedDEBIAN-CVE-2026-96637
PyPIpillow13.0.0GHSA-g842-9rc4-69pw
PyPIpillow13.0.0PYSEC-2026-4338
Ubuntu:22.04:LTSpillowno fix listedUBUNTU-CVE-2026-96637
Ubuntu:24.04:LTSpillowno fix listedUBUNTU-CVE-2026-96637
Ubuntu:26.04:LTSpillowno fix listedUBUNTU-CVE-2026-96637
Ubuntu:26.10pillowno fix listedUBUNTU-CVE-2026-96637

Affected products (as reported)

VendorProductVersions
python-pillow Pillow < 13.0.0

Weakness: CWE-400, CWE-409 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References