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High, CVSS 7.1amended

Pillow: Decompression bomb check bypass in SpiderImagePlugin.seek() leads to unbounded allocation DoS

CVE-2026-96637GHSA-g842-9rc4-69pw

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:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-96637: 0.37% estimated exploitation activity in the next 30 days; percentile 31.31 (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 SpiderImagePlugin's seek() bypasses the decompression bomb check, allowing a tiny ( DecompressionBombWarning fires correctly. - BYPASS: Image.open(stack, frame0=1x1) passes; im.seek(1) sets size (100,100) with NO DecompressionBombWarning/Error -> the check is bypassed. Real-world impact: a large frame-1 nsam/nrow (e.g. 40000x40000) causes im.load() to allocate ~6.4 GB (mode F) with the bomb check fully bypassed, from a file under 1 KB.

Suggested fix Call Image._decompression_bomb_check(self.size) at the end of SpiderImageFile._open() (or in seek() after _open()), mirroring GifImagePlugin / TiffImagePlugin. Optionally validate nsam/nrow are positive and sane in _open(). Credit: Yazan Balawneh - CyStack Security Team pillow_poc_spider_bomb.py

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-2026-96637

  2. Revision 9 · amended ·

    Amended from osv record PYSEC-2026-4338

  3. Revision 8 · amended ·

    Amended from osv record GHSA-g842-9rc4-69pw

  4. Revision 7 · amended ·

    Amended from osv record PYSEC-2026-4338

  5. Revision 6 · amended ·

    Amended from osv record GHSA-g842-9rc4-69pw

  6. Revision 5 · amended ·

    Amended from ghsa record GHSA-g842-9rc4-69pw

  7. Revision 4 · amended ·

    Amended from ghsa record GHSA-g842-9rc4-69pw

  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-g842-9rc4-69pw

  10. Revision 1 · created ·

    Published from ghsa record GHSA-g842-9rc4-69pw

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-2026-96637

Advisory: Pillow: Decompression bomb check bypass in SpiderImagePlugin.seek() leads to unbounded allocation DoS
IDs: CVE-2026-96637, GHSA-g842-9rc4-69pw
Record: https://patchnext.com/advisories/cve-2026-96637 (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-g842-9rc4-69pw (GitHub-reviewed advisory GHSA-g842-9rc4-69pw lists affected ranges: PyPI pillow >=0 <13.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-g842-9rc4-69pw (OSV record GHSA-g842-9rc4-69pw lists affected ranges: PyPI pillow >=0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/PYSEC-2026-4338 (OSV record PYSEC-2026-4338 lists affected ranges: PyPI pillow >=0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/BIT-pillow-2026-96637 (OSV record BIT-pillow-2026-96637 lists affected ranges: Bitnami pillow >=0 <13.0.0 (fixed))

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