CVE-2026-96637: pillow DoS — Fix

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.

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CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0037

Probability of exploitation

0.31%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-400 Uncontrolled Resource Consumption

CWE-409 CWE-409

Affected Products

Vendor	Product	Versions
python	pillow	< 13.0.0

References

Advisories & Patches

https://github.com/python-pillow/Pillow/commit/7cb0e02389d8aac2a60896a490f572db0b07b841 https://github.com/python-pillow/Pillow/security/advisories/GHSA-g842-9rc4-69pw

Other References

https://github.com/python-pillow/Pillow/pull/10076 https://github.com/python-pillow/Pillow/releases/tag/13.0.0

Frequently Asked Questions

What is CVE-2026-96637? +

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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-96637? +

CVE-2026-96637 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0037, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-96637? +

CVE-2026-96637 affects products from python, specifically: pillow. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-96637? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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