GHSA-w8wv-vfpc-hw2w
MEDIUMGHSA-w8wv-vfpc-hw2w is a medium-severity (CVSS 5.9) Path Traversal vulnerability in nicegui. O3 Security confirms whether GHSA-w8wv-vfpc-hw2w is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
NiceGUI: Upload filename sanitization bypass via backslashes allows path traversal on Windows
Blast Radius
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Description
Summary
The upload filename sanitization introduced in GHSA-9ffm-fxg3-xrhh uses PurePosixPath(filename).name to strip path components. Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename.
Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI's bundled examples) are vulnerable to arbitrary file write on Windows.
Details
The sanitization in nicegui/elements/upload_files.py uses:
filename = PurePosixPath(upload.filename or '').name
PurePosixPath treats backslashes as literal characters, not path separators:
>>> PurePosixPath('..\\..\\secret\\evil.txt').name
'..\\..\\secret\\evil.txt' # Not stripped!
When this filename is used in a path operation on Windows (e.g., Path('uploads') / file.name), Windows Path interprets backslashes as directory separators, resolving the path outside the intended directory.
Impact
On Windows deployments of NiceGUI applications that use file.name in path construction:
- Arbitrary file write outside the intended upload directory
- Potential remote code execution through overwriting application files or placing executables in known locations
- Data integrity loss through overwriting existing files
Linux and macOS are not affected, as they treat backslashes as literal filename characters.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | nicegui | all versions | 3.10.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nicegui. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update nicegui to 3.10.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w8wv-vfpc-hw2w 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.
How O3 protects you
O3 pinpoints whether GHSA-w8wv-vfpc-hw2w is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-w8wv-vfpc-hw2w. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-w8wv-vfpc-hw2w in your dependencies?
O3 detects GHSA-w8wv-vfpc-hw2w across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.