Pillow: Heap out-of-bounds write in ImageFilter.RankFilter via integer overflow in ImagingExpand

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.2 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

EPSS

• CVE-2026-59197: 0.45% estimated exploitation activity in the next 30 days; percentile 38.79 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Pillow's public rank-filter API can trigger a native heap out-of-bounds write when given a very large odd filter size. Minimal public API trigger: ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation. With size = 4294967295, the expansion margin is 2147483647 (INTMAX). ImagingExpand() then computes the output dimensions with unchecked signed int arithmetic. On tested builds, this wraps to a tiny output image and the border-expansion loop writes past the allocation. This is reachable through documented public classes (RankFilter, MedianFilter, MinFilter, and MaxFilter). No private API, ctypes, or custom Python object is needed. Details Current src/PIL/ImageFilter.py: The expand() call is made before image.rankfilter(...). Current src/libImaging/Filter.c:ImagingExpand() does not check output-size overflow: For a 3x3 image and xmargin = ymargin = INTMAX, the computed output size wraps to 1x1 on tested builds. The following…

Published by the source

20 Jul 2026, 23:08 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:49 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-xj96-63gp-2gmr

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-xj96-63gp-2gmr

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# Patch Next advisory brief: CVE-2026-59197

Advisory: Pillow: Heap out-of-bounds write in `ImageFilter.RankFilter` via integer overflow in `ImagingExpand`
IDs: CVE-2026-59197, GHSA-xj96-63gp-2gmr
Record: https://patchnext.com/advisories/cve-2026-59197 (revision 2, source checked 26 Oct 2026, 13:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pillow 12.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pillow: affected < 12.3.0; fixed in 12.3.0

## Suggested inspection (read-only)
- `python -m pip show pillow`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pillow.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-xj96-63gp-2gmr (OSV record GHSA-xj96-63gp-2gmr lists affected ranges: PyPI pillow >=0 <12.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-xj96-63gp-2gmr (GitHub-reviewed advisory GHSA-xj96-63gp-2gmr lists affected ranges: PyPI pillow >=0 <12.3.0)

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