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setuptools: Windows path escape via namespace_packages.txt during legacy wheel installation Description

Low severity GitHub Reviewed Published Oct 19, 2026 in pypa/setuptools • Updated Oct 23, 2026

Package

pip setuptools (pip)

Affected versions

>= 38.2.2, < 84.1.0

Patched versions

84.1.0

Description

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.

### References
- https://github.com/pypa/setuptools/security/advisories/GHSA-xmj3-9gf7-h52w
- https://github.com/pypa/setuptools/pull/5329
- https://github.com/pypa/setuptools/commit/6d07b8d17890dda58d944ac51e58f54af92d52af
- https://github.com/pypa/setuptools/releases/tag/v84.1.0
@jaraco jaraco published to pypa/setuptools Oct 19, 2026
Published to the GitHub Advisory Database Oct 23, 2026
Reviewed Oct 23, 2026
Last updated Oct 23, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity High
Attack Requirements Present
Privileges Required Low
User interaction Active
Vulnerable System Impact Metrics
Confidentiality None
Integrity Low
Availability Low
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
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

EPSS score

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-xmj3-9gf7-h52w

Source code

Credits

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