CVE-2026-42309: Pillow Pillow Has A Heap Buffer Vulnerability

MODERATE
Advisory Identifier: GHSA-5xmw-vc9v-4wf2
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CVSS 5.5
CWE-122
Published
Advisory Summary

CVE-2026-42309 is a MODERATE (CVSS 5.5) pillow has a heap buffer vulnerability (CWE-122: Heap-based Buffer Overflow) affecting Pillow libraries in the PyPI ecosystem. The issue involves pillow has a heap buffer overflow with nested list coordinates. Remediation is available by upgrading affected packages to version 12.2.0.

CVE-2026-42309 at a Glance

CVE Identifier CVE-2026-42309
GHSA Identifier GHSA-5xmw-vc9v-4wf2
Severity MODERATE
CVSS v3.1 Base Score 5.5
CWE Classification CWE-122: Heap-based Buffer Overflow
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-2026-42309

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-2026-42309, 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-122: Heap-based Buffer Overflow, where a heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). 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

Passing nested lists as coordinates to APIs that accept coordinates such as `ImagePath.Path`, `ImageDraw.ImageDraw.polygon` and `ImageDraw.ImageDraw.line` could cause a heap buffer overflow, as nested lists were recursively unpacked beyond the allocated buffer. Coordinate lists are now validated to contain exactly two numeric coordinates. This was introduced in Pillow 11.2.1.

CVE-2026-42309 Affected Pillow Versions

1 component(s)
Fixed Versions:
12.2.0
Product / Package Ecosystem Affected Versions Fixed Version
pillow
pypi/pillow
PyPI
≥ 11.2.1
< 12.2.0
12.2.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/python-pillow/Pillow/security/advisories/GHSA-5xmw-vc9v-4wf2
NVD — CVE-2026-42309 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42309
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-2026-42309?
CVE-2026-42309 is a security vulnerability in Pillow involving Pillow has a heap buffer overflow with nested list coordinates under CWE-122: Heap-based Buffer Overflow.
Which Pillow versions are affected?
Affected versions include releases prior to 12.2.0 across affected packages: pillow.
What version fixes CVE-2026-42309?
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-2026-42309?
CVE-2026-42309 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-2026-42309?
CVE-2026-42309 is classified under CWE-122: Heap-based Buffer Overflow (A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().).
How can I check PyPI dependencies for CVE-2026-42309?
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 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5xmw-vc9v-4wf2",
  "modified" : "2026-05-13T13:39:39Z",
  "published" : "2026-05-04T20:18:27Z",
  "aliases" : [ "CVE-2026-42309" ],
  "summary" : "Pillow has a heap buffer overflow with nested list coordinates",
  "details" : "Passing nested lists as coordinates to APIs that accept coordinates such as `ImagePath.Path`, `ImageDraw.ImageDraw.polygon` and `ImageDraw.ImageDraw.line` could cause a heap buffer overflow, as nested lists were recursively unpacked beyond the allocated buffer. Coordinate lists are now validated to contain exactly two numeric coordinates. This was introduced in Pillow 11.2.1.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pillow"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.2.1"
      }, {
        "fixed" : "12.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/python-pillow/Pillow/security/advisories/GHSA-5xmw-vc9v-4wf2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42309"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/python-pillow/Pillow"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/python-pillow/Pillow/releases/tag/12.2.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-122" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-04T20:18:27Z",
    "nvd_published_at" : "2026-05-09T06:16:10Z"
  }
}