Pillow has a PDF Parsing Trailer Infinite Loop (DoS)

Exploitation

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

CVSS 4.0

5.1 · CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-42310: 0.17% estimated exploitation activity in the next 30 days; percentile 6.55 (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.

Impact An attacker can supply a malicious PDF that causes the process to hang indefinitely, consuming 100% CPU and making the application unresponsive. Patches Patched version: 12.2.0. PdfParser (introduced in Pillow 4.2.0) follows Prev pointers in PDF trailers to read cross-reference sections. If a trailer's Prev pointer references an offset that has already been processed — either pointing to itself or forming a longer cycle — the parser enters an infinite loop. Pillow now tracks previously processed trailer offsets and raises an error if a cycle is detected. Workarounds Use any version but the affected versions: = 4.2.0, < 12.2.0 Resources - Fix: https://github.com/python-pillow/Pillow/pull/9519

Published by the source

4 May 2026, 20:19 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:41 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-r73j-pqj5-w3x7

2. Revision 2 · amended · 25 Oct 2026

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

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-r73j-pqj5-w3x7

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# Patch Next advisory brief: CVE-2026-42310

Advisory: Pillow has a PDF Parsing Trailer Infinite Loop (DoS)
IDs: CVE-2026-42310, GHSA-r73j-pqj5-w3x7
Record: https://patchnext.com/advisories/cve-2026-42310 (revision 3, source checked 26 Oct 2026, 13:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pillow 12.2.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pillow: affected >= 4.2.0, < 12.2.0; fixed in 12.2.0

## 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-r73j-pqj5-w3x7 (OSV record GHSA-r73j-pqj5-w3x7 lists affected ranges: PyPI pillow >=4.2.0 <12.2.0 (fixed))
- Verified: https://github.com/advisories/GHSA-r73j-pqj5-w3x7 (GitHub-reviewed advisory GHSA-r73j-pqj5-w3x7 lists affected ranges: PyPI pillow >=4.2.0 <12.2.0)

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