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High, CVSS 7.1amended

Pillow: Heap over-read in WMF/EMF rendering via 16-bit dimension truncation (Windows builds)

CVE-2026-96644GHSA-9v9v-9qvf-h2hj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (pillow 13.0.0; pillow 13.0.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Bitnami pillow

    Affected
    < 13.0.0
    Fixed in
    13.0.0

  • PyPI pillow

    Affected
    < 13.0.0
    Fixed in
    13.0.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-96644: 0.38% estimated exploitation activity in the next 30 days; percentile 32.54 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary On Windows builds, Pillow stores EMF and WMF image dimensions without a range check and passes them to the native `drawwmf` handler. That code sizes its allocation from dimensions truncated into 16-bit header fields but copies the result using the full 32-bit dimensions. A crafted metafile that is wide and short passes the decompression-bomb pixel check yet causes a heap over-read.

Details The EMF branch computes the size straight from signed 32-bit header fields and stores it with no positivity or range check: - `src/PIL/WmfImagePlugin.py:121-129` reads the bounding box; `:148` stores it; the size reaches the native handler through `src/PIL/WmfImagePlugin.py:56`. In the native handler the DIB header fields `bcWidth` and `bcHeight` are 16-bit and truncate the allocation, while the copy length uses the untruncated ints: - `src/display.c:793-794` assign the 16-bit fields - `src/display.c:800` sizes the allocation from them - `src/display.c:827` copies `height * ((width…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 10 · amended ·

    Amended from osv record BIT-pillow-2026-96644

  2. Revision 9 · amended ·

    Amended from osv record PYSEC-2026-4343

  3. Revision 8 · amended ·

    Amended from osv record GHSA-9v9v-9qvf-h2hj

  4. Revision 7 · amended ·

    Amended from osv record PYSEC-2026-4343

  5. Revision 6 · amended ·

    Amended from osv record GHSA-9v9v-9qvf-h2hj

  6. Revision 5 · amended ·

    Amended from ghsa record GHSA-9v9v-9qvf-h2hj

  7. Revision 4 · amended ·

    Amended from ghsa record GHSA-9v9v-9qvf-h2hj

  8. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  9. Revision 2 · amended ·

    Amended from osv record GHSA-9v9v-9qvf-h2hj

  10. Revision 1 · created ·

    Published from ghsa record GHSA-9v9v-9qvf-h2hj

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-96644

Advisory: Pillow: Heap over-read in WMF/EMF rendering via 16-bit dimension truncation (Windows builds)
IDs: CVE-2026-96644, GHSA-9v9v-9qvf-h2hj
Record: https://patchnext.com/advisories/cve-2026-96644 (revision 10, source checked 30 Oct 2026, 07:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pillow 13.0.0; pillow 13.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Bitnami pillow: affected < 13.0.0; fixed in 13.0.0
- PyPI pillow: affected < 13.0.0; fixed in 13.0.0

## Suggested inspection (read-only)
- Bitnami pillow: check the installed version with your package manager.
- `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://github.com/advisories/GHSA-9v9v-9qvf-h2hj (GitHub-reviewed advisory GHSA-9v9v-9qvf-h2hj lists affected ranges: PyPI pillow >=0 <13.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-9v9v-9qvf-h2hj (OSV record GHSA-9v9v-9qvf-h2hj lists affected ranges: PyPI pillow >=0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/PYSEC-2026-4343 (OSV record PYSEC-2026-4343 lists affected ranges: PyPI pillow >=0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/BIT-pillow-2026-96644 (OSV record BIT-pillow-2026-96644 lists affected ranges: Bitnami pillow >=0 <13.0.0 (fixed))

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