Briefcase: Windows MSI Installer Privilege Escalation via Insecure Directory Permissions
Impact
If a developer uses Briefcase to produce an Windows MSI installer for a project, and that project is installed for All Users (i.e., per-machine scope), the installation process creates an directory that inherits all the permissions of the parent directory. Depending on the location chosen by the installing user, this may allow a low privilege but authenticated user to replace or modify the binaries installed by the application. If an administrator then runs the altered binary, the binary will run with elevated privileges.
Patches
The problem is caused by the template used to generate the WXS file for Windows projects. It was fixed with the following PRs:
- beeware/briefcase-windows-app-template#86
- beeware/briefcase-windows-VisualStudio-template#85
These patches have been backported to the templates used in Briefcase 0.3.26, 0.4.0, and 0.4.1. Re-running briefcase create on your Briefcase project will result in the updated templates being used.
Workarounds
The change from beeware/briefcase-windows-app-template#86 can be added to any existing Briefcase .wxs file generated by Briefcase 0.3.24 or later.
Resources
beeware/briefcase#2759 is a formal bug report of the problem.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | briefcase | >= 0.3.0, < 0.3.26 | 0.3.26 |
References
- https://github.com/beeware/briefcase/issues/2759
- https://github.com/beeware/briefcase-windows-VisualStudio-template/pull/85
- https://github.com/beeware/briefcase-windows-app-template/pull/86
- https://github.com/beeware/briefcase/security/advisories/GHSA-r3r2-35v9-v238
- https://nvd.nist.gov/vuln/detail/CVE-2026-33430
- https://github.com/beeware/briefcase
- https://github.com/pypa/advisory-database/tree/main/vulns/briefcase/PYSEC-2026-27.yaml
- CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H- Weakness (CWE)
CWE-732- Platform
- Python (PyPI)
- Package
briefcase- Disclosed
- 23.03.2026
- Updated
- 11.10.2026 12:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-27 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-r3r2-35v9-v238 - CC BY 4.0
Vulnerability history: briefcase
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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