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High, CVSS 8.2amended

Pillow PDF append accepts malformed shared page-tree DAG causing resource exhaustion

CVE-2026-96640GHSA-mrfp-p49p-3hf2

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
    >= 5.1.0, < 13.0.0
    Fixed in
    13.0.0

  • PyPI pillow

    Affected
    >= 5.1.0, < 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
8.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-96640: 0.60% estimated exploitation activity in the next 30 days; percentile 48.96 (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 Pillow's documented PDF append path can spend disproportionate CPU time on a compact malformed PDF page tree. An attacker who can supply an existing PDF to an application that appends an image with `Image.save(..., format="PDF", append=True)` can provide a malformed `/Pages` tree where each level repeats the same child `/Pages` reference in `/Kids`. Pillow treats the graph as a tree and expands each repeated reference in `PdfParser.linearize_page_tree()` without tracking visited or duplicate indirect references. In the bounded proof below, a `1410`-byte PDF expands to `8192` page references from one distinct page object and takes about `9.6` seconds through the append path. A comparable linear control with the same depth stays at one page reference and completes in about `0.02` seconds. This is in scope for Pillow's security policy because it is reproducible in `main`, affects the latest public release tested (`12.3.0`), and is not just an unexpected Python exception. The…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 7 · amended ·

    Amended from osv record BIT-pillow-2026-96640

  2. Revision 6 · amended ·

    Amended from osv record GHSA-mrfp-p49p-3hf2

  3. Revision 5 · amended ·

    Amended from ghsa record GHSA-mrfp-p49p-3hf2

  4. Revision 4 · amended ·

    Amended from ghsa record GHSA-mrfp-p49p-3hf2

  5. Revision 3 · amended ·

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

  6. Revision 2 · amended ·

    Amended from osv record GHSA-mrfp-p49p-3hf2

  7. Revision 1 · created ·

    Published from ghsa record GHSA-mrfp-p49p-3hf2

Agent brief

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# Patch Next advisory brief: CVE-2026-96640

Advisory: Pillow PDF append accepts malformed shared page-tree DAG causing resource exhaustion
IDs: CVE-2026-96640, GHSA-mrfp-p49p-3hf2
Record: https://patchnext.com/advisories/cve-2026-96640 (revision 7, 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 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 13.0.0; pillow 13.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Bitnami pillow: affected >= 5.1.0, < 13.0.0; fixed in 13.0.0
- PyPI pillow: affected >= 5.1.0, < 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-mrfp-p49p-3hf2 (GitHub-reviewed advisory GHSA-mrfp-p49p-3hf2 lists affected ranges: PyPI pillow >=5.1.0 <13.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-mrfp-p49p-3hf2 (OSV record GHSA-mrfp-p49p-3hf2 lists affected ranges: PyPI pillow >=5.1.0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/BIT-pillow-2026-96640 (OSV record BIT-pillow-2026-96640 lists affected ranges: Bitnami pillow >=5.1.0 <13.0.0 (fixed))

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