How severe is CVE-2026-33430?

CVE-2026-33430 has a CVSS score of 7.3/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-33430?

CVE-2026-33430 affects the following packages: briefcase (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-33430?

Update briefcase to 0.3.26 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33430 is resolved across your whole dependency graph.

How do I detect CVE-2026-33430 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for briefcase, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-33430 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-33430 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-33430 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-33430?

CVE-2026-33430 has an EPSS (Exploit Prediction Scoring System) score of 0.1%, placing it in the 3th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-33430?

CVE-2026-33430 is classified as CWE-732 (CWE-732). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-33430 published, and has it been updated?

CVE-2026-33430 was published on March 26, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2026-33430 — briefcase

HIGHFix: beeware/briefcase-windows-VisualStudio-template#85

CVE-2026-33430 is a high-severity (CVSS 7.3) CWE-732 vulnerability in briefcase. A fix is available for briefcase — see the affected versions and patch details below.

Briefcase: Windows MSI Installer Privilege Escalation via Insecure Directory Permissions

Also known asGHSA-r3r2-35v9-v238PYSEC-2026-27

Published

Mar 26, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33430.

EPSS Exploitation Probability

via FIRST.org ↗

0.1%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs3th percentile — riskier than 3% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍briefcase

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`briefcase`	≥ 0.3.0&&< 0.3.26	0.3.26`pip install --upgrade 'briefcase==0.3.26'`

Affected Products

1 product · 1 configurations

Application

briefcasebeeware

≥ 0.3.0 && < 0.3.26

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for briefcase, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update briefcase to 0.3.26 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33430 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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