CVE-2026-42310: Pillow Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-r73j-pqj5-w3x7
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CVSS 5.5
CWE-835
Published
Advisory Summary

CVE-2026-42310 is a MODERATE (CVSS 5.5) denial of service vulnerability (CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')) affecting Pillow libraries in the PyPI ecosystem. The issue involves pillow has a pdf parsing trailer infinite loop (dos). Remediation is available by upgrading affected packages to version 12.2.0.

CVE-2026-42310 at a Glance

CVE Identifier CVE-2026-42310
GHSA Identifier GHSA-r73j-pqj5-w3x7
Severity MODERATE
CVSS v3.1 Base Score 5.5
CWE Classification CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
Affected Product Pillow
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Local (AV:L)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-42310

To remediate this vulnerability, upgrade all affected Pillow dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

pillow fixed: 12.2.0 
pip install pillow>=12.2.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show pillow

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-42310, inspect your installed packages using pip:

pip show pillow

Analyze the terminal output to locate any version of Pillow in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 12.2.0), your application is affected.

Note: The pip show pillow command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop'), where the product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. In Pillow, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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

CVE-2026-42310 Affected Pillow Versions

1 component(s)
Fixed Versions:
12.2.0
Product / Package Ecosystem Affected Versions Fixed Version
pillow
pypi/pillow
PyPI
≥ 4.2.0
< 12.2.0
12.2.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/python-pillow/Pillow/security/advisories/GHSA-r73j-pqj5-w3x7
NVD — CVE-2026-42310 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42310
Pillow Source Repository REPOSITORY
https://github.com/python-pillow/Pillow/pull/9519
Security Fix Commit FIX COMMIT
https://github.com/python-pillow/Pillow/commit/3bf614e4b8615d0ce1d5039efaf6db447fe7c468
Pillow Source Repository REPOSITORY
https://github.com/python-pillow/Pillow
Pillow Release RELEASE
https://github.com/python-pillow/Pillow/releases/tag/12.2.0

Frequently Asked Questions

What is CVE-2026-42310?
CVE-2026-42310 is a security vulnerability in Pillow involving Pillow has a PDF Parsing Trailer Infinite Loop (DoS) under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop').
Which Pillow versions are affected?
Affected versions include releases prior to 12.2.0 across affected packages: pillow.
What version fixes CVE-2026-42310?
Upgrading to 12.2.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pillow affected?
Yes, pillow is affected in releases prior to 12.2.0. Upgrade your dependency to 12.2.0 or later.
What is the CVSS score of CVE-2026-42310?
CVE-2026-42310 has a CVSS v3.1 base score of 5.5 (MODERATE) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-42310?
CVE-2026-42310 is classified under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') (The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.).
How can I check PyPI dependencies for CVE-2026-42310?
Run the dependency tree command: 'pip show pillow'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
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  "id" : "GHSA-r73j-pqj5-w3x7",
  "modified" : "2026-05-13T13:41:22Z",
  "published" : "2026-05-04T20:19:30Z",
  "aliases" : [ "CVE-2026-42310" ],
  "summary" : "Pillow has a PDF Parsing Trailer Infinite Loop (DoS)",
  "details" : "### Impact\nAn attacker can supply a malicious PDF that causes the process to hang indefinitely, consuming 100% CPU and making the application unresponsive.\n\n### Patches\nPatched version: 12.2.0.\n\nPdfParser (introduced in Pillow 4.2.0) follows Prev pointers in PDF trailers to read cross-reference sections. If a\ntrailer's Prev pointer references an offset that has already been processed — either pointing to itself or forming a\nlonger cycle — the parser enters an infinite loop. Pillow now tracks previously processed trailer offsets and raises an\nerror if a cycle is detected.\n\n### Workarounds\nUse any version but the affected versions: >= 4.2.0, < 12.2.0\n\n### Resources\n - Fix: https://github.com/python-pillow/Pillow/pull/9519",
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