CVE-2026-42311: Pillow Pillow Has An OOB Write Vulnerability

HIGH
Advisory Identifier: GHSA-pwv6-vv43-88gr
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CWE-190 CWE-787
Published
Advisory Summary

CVE-2026-42311 is a HIGH pillow has an oob write vulnerability (CWE-190: Integer Overflow or Wraparound) affecting Pillow libraries in the PyPI ecosystem. The issue involves pillow has an oob write with invalid psd tile extents (integer overflow). Remediation is available by upgrading affected packages to version 12.2.0.

CVE-2026-42311 at a Glance

CVE Identifier CVE-2026-42311
GHSA Identifier GHSA-pwv6-vv43-88gr
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-190: Integer Overflow or Wraparound
Affected Product Pillow
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-42311

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-2026-42311, 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-190: Integer Overflow or Wraparound, where the product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. this occurs when an integer value is incremented to a value that is too large to store in the associated representation. when this occurs, the value may become a very small or negative number. 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 Processing a malicious PSD file could lead to memory corruption, potentially resulting in a crash or arbitrary code execution. ### Patches Patched version: 12.2.0 Pillow 12.1.1 addressed CVE-2026-25990 by adding checks for tile extents in PSD image decoding/encoding to prevent an out-of-bounds write. However, the bounds checks computed tile extent sums using types susceptible to integer overflow, meaning a PSD image with carefully chosen tile dimensions could produce values that wrap around and bypass the checks, still triggering an out-of-bounds write in src/decode.c and src/encode.c. The fix avoids adding extents together before comparison. ### Workarounds Use any version but affected versions: >= 10.3.0, < 12.2.0 ### Resources - Fix: https://github.com/python-pillow/Pillow/pull/9520 - Original issue: CVE-2026-25990 (Pillow 12.1.1)

CVE-2026-42311 Affected Pillow Versions

1 component(s)
Fixed Versions:
12.2.0
Product / Package Ecosystem Affected Versions Fixed Version
pillow
pypi/pillow
PyPI
≥ 10.3.0
< 12.2.0
12.2.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/python-pillow/Pillow/security/advisories/GHSA-cfh3-3jmp-rvhc
GitHub Advisory / Wiki ADVISORY
https://github.com/python-pillow/Pillow/security/advisories/GHSA-pwv6-vv43-88gr
NVD — CVE-2026-42311 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42311
Pillow Source Repository REPOSITORY
https://github.com/python-pillow/Pillow/pull/9520
Security Fix Commit FIX COMMIT
https://github.com/python-pillow/Pillow/commit/58f9a1d166dcb0c274807d4423522d205b0c35ea
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-2026-42311?
CVE-2026-42311 is a security vulnerability in Pillow involving Pillow has an OOB Write with Invalid PSD Tile Extents (Integer Overflow) under CWE-190: Integer Overflow or Wraparound.
Which Pillow versions are affected?
Affected versions include releases prior to 12.2.0 across affected packages: pillow.
What version fixes CVE-2026-42311?
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 CWE is associated with CVE-2026-42311?
CVE-2026-42311 is classified under CWE-190: Integer Overflow or Wraparound (The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.).
How can I check PyPI dependencies for CVE-2026-42311?
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-pwv6-vv43-88gr",
  "modified" : "2026-05-13T13:41:29Z",
  "published" : "2026-05-04T20:20:31Z",
  "aliases" : [ "CVE-2026-42311" ],
  "summary" : "Pillow has an OOB Write with Invalid PSD Tile Extents (Integer Overflow)",
  "details" : "### Impact\nProcessing a malicious PSD file could lead to memory corruption, potentially resulting in a crash or arbitrary code execution.\n\n### Patches\nPatched version: 12.2.0\n\nPillow 12.1.1 addressed CVE-2026-25990 by adding checks for tile extents in PSD image decoding/encoding to prevent an out-of-bounds write. However, the bounds checks computed tile extent sums using types susceptible to integer overflow, meaning a PSD image with carefully chosen tile dimensions could produce values that wrap around and bypass the checks, still triggering an out-of-bounds write in src/decode.c and src/encode.c. The fix avoids adding extents together before comparison.\n\n### Workarounds\nUse any version but affected versions: >= 10.3.0, < 12.2.0\n\n### Resources\n - Fix: https://github.com/python-pillow/Pillow/pull/9520 \n - Original issue: CVE-2026-25990 (Pillow 12.1.1)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
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    },
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      "type" : "ECOSYSTEM",
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      }, {
        "fixed" : "12.2.0"
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    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
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    "type" : "WEB",
    "url" : "https://github.com/python-pillow/Pillow/security/advisories/GHSA-pwv6-vv43-88gr"
  }, {
    "type" : "ADVISORY",
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  }, {
    "type" : "WEB",
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  }, {
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  }, {
    "type" : "WEB",
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  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-190", "CWE-787" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-04T20:20:31Z",
    "nvd_published_at" : "2026-05-09T06:16:10Z"
  }
}