# CVE-2026-96640: Pillow PDF parser DoS via duplicate page references

Source: https://junglewise.ai/threats/cve-2026-96640-pillow-is-a-python-imaging-library-from-5-1-0-until-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-2026-96640 · Severity: high · CVSS 4 · Published 2026-10-21

Pillow is a Python library used to process and manipulate images, including PDFs. When appending to a maliciously crafted PDF file, Pillow fails to recognize that page references point to the same underlying content and instead treats them as separate pages, causing exponential expansion of the page tree. An attacker can exploit this with a small malformed PDF to trigger excessive CPU consumption and cause a denial of service during image save operations.

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-2026-96640 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-96640 being exploited in the wild.

**How severe is CVE-2026-96640?** High severity, with a CVSS score of 4, published 21 October 2026.

**Which products and versions are affected?** pillow (PyPI) >= 5.1.0, < 13.0.0, ECOSYSTEM:introduced=5.1.0,fixed=13.0.0; Python Pillow Pillow 5.1.0 to 12.x (before 13.0.0).

**Is there a fix for CVE-2026-96640?** 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-2026-96640 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-96640?** 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 PdfParser.linearize_page_tree() function in src/PIL/PdfParser.py does not track duplicate indirect references in the PDF /Pages graph, treating it as a tree instead. When Image.save(..., format="PDF", append=True) processes a crafted PDF where /Kids arrays contain repeated references to the same child /Pages node, the parser expands the shared subtree as distinct pages, leading to exponential page reference duplication. This causes disproportionate CPU consumption before the append operation completes. The fix, released in version 13.0.0, raises an error when a page loop is detected.

## Affected products

- python-pillow Pillow 5.1.0 to 12.x (before 13.0.0)

## Identifiers

- CVE-2026-96640
- GHSA-mrfp-p49p-3hf2

## Timeline

- 2026-10-21: disclosed
- 2026-10-02: patched

## References

- [https://github.com/python-pillow/Pillow/commit/6f0e7ee1f9c2fe227906f8a4b926e6622b702bc7](https://github.com/python-pillow/Pillow/commit/6f0e7ee1f9c2fe227906f8a4b926e6622b702bc7)
- [https://github.com/python-pillow/Pillow/pull/10093](https://github.com/python-pillow/Pillow/pull/10093)

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- [Pillow memory denial of service in TIFF and EXIF parsing](https://junglewise.ai/threats/cve-2026-128066-pillow-memory-dos-in-tiff-and-exif-ifd-parsing-via-overlapping)
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