Pillow: MSP RLE decoder expands a tiny file into unbounded memory

ALTO 7.5CVE-2026-112892 · BIT-pillow-2026-112892 · GHSA-gg2r-wvfm-q9rx · Published 19/10/2026 · updated 27/10/2026

Package	Affected versions	Patched versions
pillow PyPI	`≥ 4.1.0, < 13.0.0`	`13.0.0`
pillow python	`≥ 4.1.0, < 13.0.0`	`13.0.0`

Description

Summary

The MSP RLE decoder expands run-length data into an in-memory buffer with no cap tied to the declared image size. A small file that passes the pixel-count check can force hundreds of megabytes or more of allocation when the application loads pixels.

Details

The MSP decoder writes each run into an unbounded io.BytesIO and can expand roughly 85x per run:

src/PIL/MspImagePlugin.py:144-146

Impact

Memory-exhaustion denial of service from a tiny crafted image in any application that loads pixels. The expansion is decoupled from the declared pixel count, so MAX_IMAGE_PIXELS does not bound it.

NVD description

Pillow is a Python imaging library. From 4.1.0 until 13.0.0, Pillow's MSP RLE decoder can expand a small file into an unbounded in-memory buffer. The decoder writes run-length output to BytesIO without limiting expansion to the declared image size. An attacker can supply a crafted MSP image to an application that loads its pixels. This can exhaust memory and deny service even when the declared pixel count passes the decompression-bomb check. This issue is fixed in version 13.0.0.

References

python-pillow/Pillow security advisory · WEB
nvd.nist.gov/vuln/detail/CVE-2026-112892 · ADVISORY
python-pillow/Pillow commit 5dcb630 · WEB
python-pillow/Pillow · PACKAGE
python-pillow/Pillow release 13.0.0 · WEB

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Package

Affected versions

Patched versions

pillow

PyPI

≥ 4.1.0, < 13.0.0

13.0.0

pillow

python

≥ 4.1.0, < 13.0.0

13.0.0

Description

Summary

Details

The MSP decoder writes each run into an unbounded io.BytesIO and can expand roughly 85x per run:

src/PIL/MspImagePlugin.py:144-146

Impact

Memory-exhaustion denial of service from a tiny crafted image in any application that loads pixels. The expansion is decoupled from the declared pixel count, so MAX_IMAGE_PIXELS does not bound it.

NVD description