FITS GZIP decompression bomb in Pillow

ALTO 7.5CVE-2026-40192 · BIT-pillow-2026-40192 · GHSA-whj4-6x5x-4v2j · Published 15/04/2026 · updated 26/10/2026

Package	Affected versions	Patched versions
pillow PyPI	`≥ 10.3.0, < 12.2.0`	`12.2.0`
pillow python	`≥ 10.3.0, < 12.2.0`	`12.2.0`

Description

Impact

Pillow did not limit the amount of GZIP-compressed data read when decoding a FITS image, making it vulnerable to decompression bomb attacks. A specially crafted FITS file could cause unbounded memory consumption, leading to denial of service (OOM crash or severe performance degradation).

Patches

The amount of data read is now limited to the necessary amount. Fixed in Pillow 12.2.0 (PR #9521).

Workarounds

Avoid Pillow >= 10.3.0, < 12.2.0 Only open specific image formats, excluding FITS.

NVD description

Pillow is a Python imaging library. Versions 10.3.0 through 12.1.1 did not limit the amount of GZIP-compressed data read when decoding a FITS image, making them vulnerable to decompression bomb attacks. A specially crafted FITS file could cause unbounded memory consumption, leading to denial of service (OOM crash or severe performance degradation). If users are unable to immediately upgrade, they should only open specific image formats, excluding FITS, as a workaround.

References

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