CVE-2026-33430: Briefcase Windows MSI Installer Privilege Escalation via Insecure Directory Permissions
Summary
CVE-2026-33430: Briefcase: Windows MSI Installer Privilege Escalation via Insecure Directory Permissions. Affects briefcase versions >= 0.3.0, < 0.3.26. Fixed in 0.3.26. How to fix ↓
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Background
Briefcase is a tool used by developers to package Python applications into standalone executables. It simplifies the process of creating installers for various platforms, including Windows. The tool is designed to support multiple application formats and provides a user-friendly interface for managing project dependencies and configurations. However, a vulnerability exists in the way Briefcase generates Windows MSI installers, specifically when installed for all users, which can lead to privilege escalation.
Vulnerability Detail
The vulnerability arises from the creation of a directory during the installation process that inherits permissions from its parent directory. If a low-privileged but authenticated user modifies or replaces the binaries in this directory, an administrator running the altered binary will execute it with elevated privileges. This could potentially allow unauthorized access to sensitive operations or data, making it a significant security risk.
How To Fix
Minimum fixed version
0.3.26
This is the first release that contains the fix.
pip install --upgrade "briefcase==0.3.26"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
If you are unable to upgrade immediately, you can manually modify the existing .wxs file generated by Briefcase 0.3.24 or later. Incorporate the changes from the pull request beeware/briefcase-windows-app-template#86 to enhance security.
Conclusion
In summary, the vulnerability identified as CVE-2026-33430 in Briefcase poses a significant risk due to insecure directory permissions during the installation of Windows MSI installers. Developers are encouraged to update to the patched version or apply the necessary workarounds to mitigate this risk.
See every vulnerability recorded for briefcase →
FAQ
The vulnerability allows low-privileged users to modify application binaries, which can lead to privilege escalation when an administrator runs the altered binaries.
You can use Vulert's playground at Vulert Scanner to check if your application is impacted by this vulnerability without needing to sign up.
Briefcase versions prior to 0.3.26 are affected by this vulnerability.
The CVSS score for this vulnerability is 7.3, indicating a high severity level.
If upgrading is not an option, you can manually apply the security changes to your existing .wxs files as a temporary workaround.
