Vulnerability-Lookup

PYSEC-2026-4339

Vulnerability from pysec - Published: 2026-10-21 21:20 - Updated: 2026-10-28 10:34

Details

Pillow is a Python imaging library. From 11.0.0 until 13.0.0, multi-frame loaders can retain an ImagingCore allocation created for a narrow frame mode while a later frame of the same dimensions changes the logical mode and decoder tiles to wider RGB or CMYK data. ImageFile.load_prepare() reuses the stale native storage because _im is non-null without verifying that its mode and size still match. Crafted PSD, MPO, DCX, or MIC frame transitions can then write wider pixels into the narrow allocation, causing native out-of-bounds writes and crashes. The MPO path can also cause a native over-read and, in demonstrated runtime-specific profiles, command execution. This issue is fixed in version 13.0.0.

Severity

9.8 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Impacted products

Name	purl
pillow	pkg:pypi/pillow

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "pillow",
        "purl": "pkg:pypi/pillow"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "11.0.0"
            },
            {
              "fixed": "13.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "11.0.0",
        "11.1.0",
        "11.2.1",
        "11.3.0",
        "12.0.0",
        "12.1.0",
        "12.1.1",
        "12.2.0",
        "12.3.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-96639",
    "GHSA-v9pv-5gc8-w2m6"
  ],
  "details": "Pillow is a Python imaging library. From 11.0.0 until 13.0.0, multi-frame loaders can retain an ImagingCore allocation created for a narrow frame mode while a later frame of the same dimensions changes the logical mode and decoder tiles to wider RGB or CMYK data. ImageFile.load_prepare() reuses the stale native storage because _im is non-null without verifying that its mode and size still match. Crafted PSD, MPO, DCX, or MIC frame transitions can then write wider pixels into the narrow allocation, causing native out-of-bounds writes and crashes. The MPO path can also cause a native over-read and, in demonstrated runtime-specific profiles, command execution. This issue is fixed in version 13.0.0.",
  "id": "PYSEC-2026-4339",
  "modified": "2026-10-28T10:34:04.790311Z",
  "published": "2026-10-21T21:20:32.217Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/python-pillow/Pillow/releases/tag/13.0.0"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/python-pillow/Pillow/security/advisories/GHSA-v9pv-5gc8-w2m6"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/python-pillow/Pillow/pull/10105"
    },
    {
      "type": "FIX",
      "url": "https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-96639 (GCVE-0-2026-96639)

Vulnerability from cvelistv5 – Published: 2026-10-21 21:06 – Updated: 2026-10-21 21:06

Title

Pillow multi-frame loaders can reuse stale native image storage after mode transitions

Summary

Severity

9.8 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE

CWE-125 - Out-of-bounds Read
CWE-787 - Out-of-bounds Write

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7926 records in the last 180 days details

References

4 references

URL	Tags
https://github.com/python-pillow/Pillow/security/…	x_refsource_CONFIRM
https://github.com/python-pillow/Pillow/pull/10105	x_refsource_MISC
https://github.com/python-pillow/Pillow/commit/78…	x_refsource_MISC
https://github.com/python-pillow/Pillow/releases/…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
python-pillow	Pillow	Affected: >= 11.0.0, < 13.0.0

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "Pillow",
          "vendor": "python-pillow",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 11.0.0, \u003c 13.0.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Pillow is a Python imaging library. From 11.0.0 until 13.0.0, multi-frame loaders can retain an ImagingCore allocation created for a narrow frame mode while a later frame of the same dimensions changes the logical mode and decoder tiles to wider RGB or CMYK data. ImageFile.load_prepare() reuses the stale native storage because _im is non-null without verifying that its mode and size still match. Crafted PSD, MPO, DCX, or MIC frame transitions can then write wider pixels into the narrow allocation, causing native out-of-bounds writes and crashes. The MPO path can also cause a native over-read and, in demonstrated runtime-specific profiles, command execution. This issue is fixed in version 13.0.0."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-125",
              "description": "CWE-125: Out-of-bounds Read",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-787",
              "description": "CWE-787: Out-of-bounds Write",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T21:06:42.111Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/python-pillow/Pillow/security/advisories/GHSA-v9pv-5gc8-w2m6",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/python-pillow/Pillow/security/advisories/GHSA-v9pv-5gc8-w2m6"
        },
        {
          "name": "https://github.com/python-pillow/Pillow/pull/10105",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/python-pillow/Pillow/pull/10105"
        },
        {
          "name": "https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a"
        },
        {
          "name": "https://github.com/python-pillow/Pillow/releases/tag/13.0.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/python-pillow/Pillow/releases/tag/13.0.0"
        }
      ],
      "source": {
        "advisory": "GHSA-v9pv-5gc8-w2m6",
        "discovery": "UNKNOWN"
      },
      "title": "Pillow multi-frame loaders can reuse stale native image storage after mode transitions"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-96639",
    "datePublished": "2026-10-21T21:06:42.111Z",
    "dateReserved": "2026-09-23T14:35:50.130Z",
    "dateUpdated": "2026-10-21T21:06:42.111Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

GHSA-V9PV-5GC8-W2M6

Vulnerability from github – Published: 2026-10-22 16:00 – Updated: 2026-10-22 16:00

Summary

Pillow multi-frame loaders can reuse stale native image storage after mode transitions

Details

Summary

Pillow multi-frame image loaders can retain native ImagingCore storage allocated for one frame while changing the Python-side image mode and decoder tiles for a later frame.

If frame 0 allocates storage for a narrow mode such as L, and a later frame of the same dimensions switches to a wider mode such as RGB or CMYK, Pillow may decode wider pixels into the stale narrow native buffer. This causes native out-of-bounds writes and process crashes. In the MPO/JPEG path, I also demonstrated command execution in matching Python/Pillow runtime profiles through Pillow's documented ImageSequence.Iterator + frame.load() path.

Details

The root cause appears to be that ImageFile.load_prepare() only reallocates native storage when _im is None. It does not verify that the retained native ImagingCore storage still matches self.mode and self.size.

Several multi-frame seek() / _open() paths can update self._mode and decoder tiles for a later frame without invalidating _im. The decoder then writes or reads according to the new frame mode while the native storage still belongs to the old frame mode.

Verified affected surfaces:

PSD

PsdImageFile.seek() can switch from grayscale/native L storage to RGB layer decoding while retaining _im. This produces attacker-controlled native out-of-bounds writes and reliable crashes.

MPO/JPEG

A crafted two-frame MPO can make frame 0 allocate L storage, then make frame 1 decode CMYK / RGB data into the retained L storage. The documented ImageSequence.Iterator path reaches this with frame.load(). Verified native memory corruption, crash, over-read behavior, and scoped harmless-marker command execution on Pillow 12.3.0.

DCX

DcxImageFile.seek() calls PcxImageFile._open(), which changes mode/tile state without a native-storage mode guard. A crafted DCX with L then RGB PCX frames produces retained-storage mismatch and crash.

MIC

MIC can call TiffImageFile._open() directly and bypass TIFF's normal guarded seek() behavior. With a NextIFD-based reachable frame transition, this produces retained-storage mismatch and crash.

TIFF appears to be a useful positive control because its seek() path checks both size and mode before reusing storage.

Impact

process crash / denial of service,
native out-of-bounds write,
native over-read in the MPO path.

Stronger proven impact:

command execution in matching Python/Pillow runtime profiles through the MPO/JPEG path.

Server-side deployment impact:

Create a local vulnerable web upload service that accepts an unauthenticated MPO upload and automatically processes it with Pillow.
The attack is one HTTP request and requires no user interaction after upload.
The fixed harmless command-output marker succeeded 10/10 times.
The _im=None control was clean 10/10 times.

Reproduction Evidence

Tested version:

Pillow 12.3.0

MPO terminal proof environments:

Python 3.12.3 + Pillow 12.3.0, clean PyPI environment:
marker 10/10, control 0/10

Python 3.13.14 + Pillow 12.3.0, prepared profile:
marker 10/10, control 0/10

Server-side web-upload proof:

control 1..10: MARKER_MISSING
control_summary ok 0 missing 10 /10

vulnerable 1..10: MARKER_OK marker_output <server-user>
vulnerable_summary ok 10 missing 0 /10

The terminal proof uses a fixed harmless marker command only. It does not use a reverse shell, persistence, data exfiltration, or arbitrary attacker-selected commands.

I can provide the following private artifacts to maintainers:

minimal crash fixtures for PSD, MPO, DCX, and MIC,
non-weaponized MPO marker PoC,
local vulnerable web upload demo,
gdb/GEF geometry receipts,
control-run logs,
proposed regression-test shape.

Minimal Reproduction Shape

For the MPO path, the vulnerable consumer shape is:

from io import BytesIO
from PIL import Image, ImageSequence

source = BytesIO(open(path, "rb").read())
image = Image.open(source)
iterator = ImageSequence.Iterator(image)
next(iterator).load()
next(iterator).load()

The crafted image shape is:

frame 0: mode L, dimensions W x H
frame 1: same W x H, wider mode such as CMYK

Frame 0 allocates native L storage. Frame 1 changes the logical mode and decoder state but can reuse the old native storage. The frame 1 decoder writes using the wider mode into the narrow storage.

Suggested Fix Direction

Before reusing native ImagingCore storage, Pillow should verify that the retained storage is compatible with the current logical image mode and size.

A central guard in ImageFile.load_prepare() could compare native storage mode/size against self.mode / self.size and allocate fresh storage when they differ. Alternatively, every mode-changing seek() / _open() path should explicitly invalidate _im before decoding.

Caution: TIFF has specialized tile-size behavior and already has a mode/size guard, so a central fix should avoid regressing TIFF tile-buffer handling.

Credit

Rotem Kama

Methodology Note

AI-assisted analysis was used for discovery and verification support. Claims in this report are limited to the local artifacts, controls, and command outputs described above.

Severity

9.8 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "Pillow"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "11.0.0"
            },
            {
              "fixed": "13.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-96639"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-125",
      "CWE-787"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-22T16:00:15Z",
    "nvd_published_at": "2026-10-21T21:20:32Z",
    "severity": "CRITICAL"
  },
  "details": "### Summary\nPillow multi-frame image loaders can retain native `ImagingCore` storage allocated for one frame while changing the Python-side image `mode` and decoder tiles for a later frame.\n\nIf frame 0 allocates storage for a narrow mode such as `L`, and a later frame of the same dimensions switches to a wider mode such as `RGB` or `CMYK`, Pillow may decode wider pixels into the stale narrow native buffer. This causes native\nout-of-bounds writes and process crashes. In the MPO/JPEG path, I also demonstrated command execution in matching Python/Pillow runtime profiles through Pillow\u0027s documented `ImageSequence.Iterator` + `frame.load()` path.\n\n### Details\nThe root cause appears to be that `ImageFile.load_prepare()` only reallocates native storage when `_im is None`. It does not verify that the retained native `ImagingCore` storage still matches `self.mode` and `self.size`.\n\nSeveral multi-frame `seek()` / `_open()` paths can update `self._mode` and decoder tiles for a later frame without invalidating `_im`. The decoder then writes or reads according to the new frame mode while the native storage still belongs to the old frame mode.\n\nVerified affected surfaces:\n\n1. **PSD**\n\n   `PsdImageFile.seek()` can switch from grayscale/native `L` storage to RGB layer decoding while retaining `_im`. This produces attacker-controlled native out-of-bounds writes and reliable crashes.\n\n2. **MPO/JPEG**\n\n   A crafted two-frame MPO can make frame 0 allocate `L` storage, then make frame 1 decode `CMYK` / `RGB` data into the retained `L` storage. The documented `ImageSequence.Iterator` path reaches this with `frame.load()`.\n   Verified native memory corruption, crash, over-read behavior, and scoped harmless-marker command execution on Pillow 12.3.0.\n\n3. **DCX**\n\n   `DcxImageFile.seek()` calls `PcxImageFile._open()`, which changes mode/tile  state without a native-storage mode guard. A crafted DCX with `L` then `RGB` PCX frames produces retained-storage mismatch and crash.\n\n4. **MIC**\n\n   MIC can call `TiffImageFile._open()` directly and bypass TIFF\u0027s normal guarded `seek()` behavior. With a `NextIFD`-based reachable frame transition, this produces retained-storage mismatch and crash.\n\nTIFF appears to be a useful positive control because its `seek()` path checks\nboth size and mode before reusing storage.\n\n### Impact\n- process crash / denial of service,\n- native out-of-bounds write,\n- native over-read in the MPO path.\n\nStronger proven impact:\n\n- command execution in matching Python/Pillow runtime profiles through the MPO/JPEG path.\n\nServer-side deployment impact:\n\n- Create a local vulnerable web upload service that accepts an unauthenticated MPO upload and automatically processes it with Pillow.\n- The attack is one HTTP request and requires no user interaction after upload.\n- The fixed harmless command-output marker succeeded 10/10 times.\n- The `_im=None` control was clean 10/10 times.\n\n\n## Reproduction Evidence\n\nTested version:\n\n```text\nPillow 12.3.0\n```\n\nMPO terminal proof environments:\n\n```text\nPython 3.12.3 + Pillow 12.3.0, clean PyPI environment:\nmarker 10/10, control 0/10\n\nPython 3.13.14 + Pillow 12.3.0, prepared profile:\nmarker 10/10, control 0/10\n```\n\nServer-side web-upload proof:\n\n```text\ncontrol 1..10: MARKER_MISSING\ncontrol_summary ok 0 missing 10 /10\n\nvulnerable 1..10: MARKER_OK marker_output \u003cserver-user\u003e\nvulnerable_summary ok 10 missing 0 /10\n```\n\nThe terminal proof uses a fixed harmless marker command only. It does not use a reverse shell, persistence, data exfiltration, or arbitrary attacker-selected commands.\n\nI can provide the following private artifacts to maintainers:\n\n- minimal crash fixtures for PSD, MPO, DCX, and MIC,\n- non-weaponized MPO marker PoC,\n- local vulnerable web upload demo,\n- gdb/GEF geometry receipts,\n- control-run logs,\n- proposed regression-test shape.\n\n## Minimal Reproduction Shape\n\nFor the MPO path, the vulnerable consumer shape is:\n\n```python\nfrom io import BytesIO\nfrom PIL import Image, ImageSequence\n\nsource = BytesIO(open(path, \"rb\").read())\nimage = Image.open(source)\niterator = ImageSequence.Iterator(image)\nnext(iterator).load()\nnext(iterator).load()\n```\n\nThe crafted image shape is:\n\n```text\nframe 0: mode L, dimensions W x H\nframe 1: same W x H, wider mode such as CMYK\n```\n\nFrame 0 allocates native `L` storage. Frame 1 changes the logical mode and decoder state but can reuse the old native storage. The frame 1 decoder writes using the wider mode into the narrow storage.\n\n## Suggested Fix Direction\n\nBefore reusing native `ImagingCore` storage, Pillow should verify that the retained storage is compatible with the current logical image mode and size.\n\nA central guard in `ImageFile.load_prepare()` could compare native storage mode/size against `self.mode` / `self.size` and allocate fresh storage when they differ. Alternatively, every mode-changing `seek()` / `_open()` path should explicitly invalidate `_im` before decoding.\n\nCaution: TIFF has specialized tile-size behavior and already has a mode/size guard, so a central fix should avoid regressing TIFF tile-buffer handling.\n\n\n## Credit\n\n```text\nRotem Kama\n```\n\n## Methodology Note\n\nAI-assisted analysis was used for discovery and verification support. Claims in this report are limited to the local artifacts, controls, and command outputs described above.",
  "id": "GHSA-v9pv-5gc8-w2m6",
  "modified": "2026-10-22T16:00:15Z",
  "published": "2026-10-22T16:00:15Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/security/advisories/GHSA-v9pv-5gc8-w2m6"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-96639"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/pull/10105"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/commit/78d97d994579aef81aafe123773d525f40f2522a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/python-pillow/Pillow"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-pillow/Pillow/releases/tag/13.0.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Pillow multi-frame loaders can reuse stale native image storage after mode transitions"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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PYSEC-2026-4339

CVE-2026-96639 (GCVE-0-2026-96639)

GHSA-V9PV-5GC8-W2M6

Summary

Details

Impact

Reproduction Evidence

Minimal Reproduction Shape

Suggested Fix Direction

Credit

Methodology Note

Tags

Sightings

Nomenclature

Vulnerability timeline

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