CVE-2026-96639: CWE-125: Out-of-bounds Read in python-pillow Pillow

Pillow versions from 11.0.0 up to but not including 13.0.0 contain a vulnerability where multi-frame loaders retain ImagingCore allocations created for narrow frame modes while later frames switch to wider RGB or CMYK modes. The ImageFile.load_prepare() function reuses stale native storage without verifying mode and size consistency, allowing crafted PSD, MPO, DCX, or MIC frames to write wider pixel data into insufficiently sized allocations. This causes native out-of-bounds writes and crashes. Additionally, the MPO processing path can trigger native out-of-bounds reads and has been demonstrated to enable command execution in specific runtime profiles. The vulnerability is tracked as CVE-2026-96639 and is fixed in Pillow 13.0.0.

Successful exploitation can lead to application crashes due to out-of-bounds memory writes and reads. In certain runtime environments, exploitation of the MPO image path can result in arbitrary command execution, posing a critical security risk. The vulnerability affects confidentiality, integrity, and availability of systems processing maliciously crafted images with vulnerable Pillow versions.

Upgrade Pillow to version 13.0.0 or later, where this vulnerability is fixed. No other mitigations are indicated by the vendor advisory. Patch status is confirmed fixed in 13.0.0.