# CVE-2026-96637: Pillow memory exhaustion via SPIDER image mode F frame

Source: https://junglewise.ai/threats/cve-2026-96637-pillow-is-a-python-imaging-library-prior-to-13-0-0  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-21. Updated: 2026-10-21  
License: CC BY 4.0 with a link back

CVE-2026-96637 · Severity: high · CVSS 4 · Published 2026-10-21

Pillow, a popular Python image processing library, contains a flaw in how it handles SPIDER-format image files. An attacker can craft a malicious image that passes initial validation with a small first frame, but then declares extremely large dimensions in a later frame, causing the application to allocate gigabytes of memory and exhaust system resources.

Technologies: [pillow (PyPI)](https://junglewise.ai/threats/technologies/pillow), [Python Pillow Pillow](https://junglewise.ai/threats/technologies/python-pillow-pillow). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi), [Python Pillow](https://junglewise.ai/threats/vendors/python-pillow).

## Quick answers

**Is CVE-2026-96637 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-96637 being exploited in the wild.

**How severe is CVE-2026-96637?** High severity, with a CVSS score of 4, published 21 October 2026.

**Which products and versions are affected?** pillow (PyPI) < 13.0.0, ECOSYSTEM:introduced=0,fixed=13.0.0; Python Pillow Pillow prior to 13.0.0.

**Is there a fix for CVE-2026-96637?** Yes. pillow (PyPI): upgrade to 13.0.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-96637 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-96637?** Check whether you run pillow (PyPI) or Python Pillow Pillow at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- pillow (PyPI): upgrade to 13.0.0 or later

  ```sh
  pip install "pillow>=13.0.0"
  ```


## Technical details

The SpiderImageFile.seek() method in SpiderImagePlugin.py reparses later SPIDER stack frames and updates image dimensions without re-running the decompression bomb check. An attacker can pass a small, valid first frame through Image.open(), then use a mode F frame to declare arbitrarily large dimensions, causing allocation of approximately four bytes per declared pixel without validation.

## Affected products

- Python Pillow Pillow prior to 13.0.0

## Identifiers

- CVE-2026-96637
- BIT-PILLOW-2026-96637
- GHSA-g842-9rc4-69pw
- PYSEC-2026-4338

## Timeline

- 2026-10-21: disclosed
- 2026-09-29: patched

## References

- [https://github.com/python-pillow/Pillow/commit/7cb0e02389d8aac2a60896a490f572db0b07b841](https://github.com/python-pillow/Pillow/commit/7cb0e02389d8aac2a60896a490f572db0b07b841)
- [https://github.com/python-pillow/Pillow/pull/10076](https://github.com/python-pillow/Pillow/pull/10076)

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