GHSA-XMJ3-9GF7-H52W

Vulnerability from github – Published: 2026-10-23 21:44 – Updated: 2026-10-23 21:44
VLAI
Summary
setuptools: Windows path escape via namespace_packages.txt during legacy wheel installation Description
Details

Summary

On Windows, attacker-controlled content in a wheel's .dist-info/namespace_packages.txt can cause setuptools' legacy wheel installation path to create an __init__.py outside the requested destination_eggdir.

The attacker can influence the destination path, but not the contents of the created file.

Details

Tested setuptools commit:

6ead555c5fb29bc57fe6105b1bffc163f56fd558

Relevant source:

setuptools/wheel.py

SHA-256:

359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd

The relevant call path is:

Wheel(wheel_path).install_as_egg(destination) → _install_as_egg → _convert_metadata → _fix_namespace_packages

A wheel can provide attacker-controlled content in:

<distribution>.dist-info/namespace_packages.txt

The namespace value is eventually used approximately as:

mod_dir = os.path.join(destination_eggdir, *mod.split('.'))
mod_init = os.path.join(mod_dir, '__init__.py')

If mod is a Windows drive-qualified absolute path containing no dots,
mod.split('.') preserves it as a single component.
On Windows, os.path.join(destination_eggdir, absolute_component) discards
the original base directory and resolves to the attacker-supplied absolute
path.
The existing wheel filename and ZIP traversal checks do not validate this
metadata value before it is subsequently interpreted as a filesystem path.

```markdown
### PoC

The reproduction was performed entirely inside a disposable temporary
directory.

Layout:

```text
sandbox/
    destination/
    outside/
    input/
    canary.txt

A synthetic wheel was created containing:

demo_pkg-1.0.dist-info/namespace_packages.txt

whose content was the absolute path of:

sandbox\outside

The real acquired setuptools implementation was then invoked:

setuptools.wheel.Wheel(synthetic_wheel).install_as_egg(
    sandbox_destination
)

The operation completed without exception.

Expected metadata was created under:

sandbox\destination\EGG-INFO

but setuptools also created:

sandbox\outside\__init__.py

The file did not exist before execution.

Its contents were:

__import__('pkg_resources').declare_namespace(__name__)

The unrelated canary remained byte-identical.

The sandbox was deleted after recording the evidence. ```

Impact

A crafted wheel can cause setuptools to create a fixed-content __init__.py outside the intended installation directory at a filesystem path influenced by the wheel, with the permissions of the process performing the installation.

The demonstrated reproduction required the target parent directory to already exist.

Severity
1.0 (Low)
CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:A/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "setuptools"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "38.2.2"
            },
            {
              "fixed": "84.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-23T21:44:11Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "### Summary\n\nOn Windows, attacker-controlled content in a wheel\u0027s\n`.dist-info/namespace_packages.txt` can cause setuptools\u0027 legacy wheel\ninstallation path to create an `__init__.py` outside the requested\n`destination_eggdir`.\n\nThe attacker can influence the destination path, but not the contents of\nthe created file.\n\n### Details\n\nTested setuptools commit:\n\n`6ead555c5fb29bc57fe6105b1bffc163f56fd558`\n\nRelevant source:\n\n`setuptools/wheel.py`\n\nSHA-256:\n\n`359b7e0d5dd8c3135653abe08a8ed5dc0352eadfd7df22cb5e2b5303b7c3cafd`\n\nThe relevant call path is:\n\n`Wheel(wheel_path).install_as_egg(destination)`\n\u2192 `_install_as_egg`\n\u2192 `_convert_metadata`\n\u2192 `_fix_namespace_packages`\n\nA wheel can provide attacker-controlled content in:\n\n`\u003cdistribution\u003e.dist-info/namespace_packages.txt`\n\nThe namespace value is eventually used approximately as:\n\n```python\nmod_dir = os.path.join(destination_eggdir, *mod.split(\u0027.\u0027))\nmod_init = os.path.join(mod_dir, \u0027__init__.py\u0027)\n\nIf mod is a Windows drive-qualified absolute path containing no dots,\nmod.split(\u0027.\u0027) preserves it as a single component.\nOn Windows, os.path.join(destination_eggdir, absolute_component) discards\nthe original base directory and resolves to the attacker-supplied absolute\npath.\nThe existing wheel filename and ZIP traversal checks do not validate this\nmetadata value before it is subsequently interpreted as a filesystem path.\n\n```markdown\n### PoC\n\nThe reproduction was performed entirely inside a disposable temporary\ndirectory.\n\nLayout:\n\n```text\nsandbox/\n    destination/\n    outside/\n    input/\n    canary.txt\n```\n\nA synthetic wheel was created containing:\n\n`demo_pkg-1.0.dist-info/namespace_packages.txt`\n\nwhose content was the absolute path of:\n\n`sandbox\\outside`\n\nThe real acquired setuptools implementation was then invoked:\n\n```python\nsetuptools.wheel.Wheel(synthetic_wheel).install_as_egg(\n    sandbox_destination\n)\n```\n\nThe operation completed without exception.\n\nExpected metadata was created under:\n\n`sandbox\\destination\\EGG-INFO`\n\nbut setuptools also created:\n\n`sandbox\\outside\\__init__.py`\n\nThe file did not exist before execution.\n\nIts contents were:\n\n```python\n__import__(\u0027pkg_resources\u0027).declare_namespace(__name__)\n```\n\nThe unrelated canary remained byte-identical.\n\nThe sandbox was deleted after recording the evidence.\n```\n\n\n### Impact\n\nA crafted wheel can cause setuptools to create a fixed-content\n`__init__.py` outside the intended installation directory at a\nfilesystem path influenced by the wheel, with the permissions of the\nprocess performing the installation.\n\nThe demonstrated reproduction required the target parent directory to\nalready exist.",
  "id": "GHSA-xmj3-9gf7-h52w",
  "modified": "2026-10-23T21:44:11Z",
  "published": "2026-10-23T21:44:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/pypa/setuptools/security/advisories/GHSA-xmj3-9gf7-h52w"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/setuptools/pull/5329"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/setuptools/commit/6d07b8d17890dda58d944ac51e58f54af92d52af"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pypa/setuptools"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/setuptools/releases/tag/v84.1.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:A/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "setuptools: Windows path escape via namespace_packages.txt during legacy wheel installation  Description"
}



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