CVE-2026-96639: Pillow multi-frame loaders can reuse stale native image storage after mode transitions

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog. That can change quickly after a public write-up; re-check if you are affected.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Editorial verdict: Patch this week. Pillow 13.0.0: Critical Image-Parsing Memory Bugs Fixed — If your service opens images that users or the internet supply, move to Pillow 13.0.0 this week; the worst bugs are memory corruption reachable from a crafted file, and reproducers are in the published advisories.

What it is

Pillow is a Python imaging library. From 11.0.0 until 13.0.0, multi-frame loaders can retain an ImagingCore allocation created for a narrow frame mode while a later frame of the same dimensions changes the logical mode and decoder tiles to wider RGB or CMYK data. ImageFile.loadprepare() reuses the stale native storage because im is non-null without verifying that its mode and size still match. Crafted PSD, MPO, DCX, or MIC frame transitions can then write wider pixels into the narrow allocation, causing native out-of-bounds writes and crashes. The MPO path can also cause a native over-read and, in demonstrated runtime-specific profiles, command execution. This issue is fixed in version 13.0.0.

Weakness type: CWE-125, CWE-787.

Product: python-pillow Pillow · Assigned by: GitHub_M · Published: 2026-10-21

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).

Timeline

• 2026-10-16 — erroneo.us brief: Pillow 13.0.0: Critical Image-Parsing Memory Bugs Fixed
• 2026-10-21 — CVE record last updated
• 2026-10-21 — CVE record published by GitHub_M

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. CVE.org record CVE-2026-96639 cve.org
2. NVD entry CVE-2026-96639 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

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