GHSA-4mh3-h929-w968
HIGHFile Browser has a Path-Based Access Control Bypass via Multiple Leading Slashes in URL
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/filebrowser/filebrowser/v2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
An authenticated user can bypass the application's "Disallow" file path rules by modifying the request URL. By adding multiple slashes (e.g., //private/) to the path, the authorization check fails to match the rule, while the underlying filesystem resolves the path correctly, granting unauthorized access to restricted files.
Details
The vulnerability allows users to bypass "Disallow" rules defined by administrators.
The issue stems from how the application handles URL path normalization and rule matching:
- Router Configuration: The router in
http/http.gois configured withr.SkipClean(true). This prevents the automatic collapse of multiple slashes (e.g., // becoming /) before the request reaches the handler. - Insecure Rule Matching: The rule enforcement logic in
rules/rules.gorelies on a simple string prefix match:strings.HasPrefix(path, r.Path). If a rule disallows /private, a request for //private fails this check because //private does not strictly start with /private. - Filesystem Resolution: After bypassing the rule check, the non-normalized path is passed to the filesystem. The filesystem treats the multiple slashes as a single separator, successfully resolving //private/secret.txt and serving the file.
PoC
The following steps demonstrate the vulnerability:
- Setup:
- Admin user creates a folder /private and adds a file /private/secret.txt. <img width="971" height="719" alt="Screenshot_20260123_151608" src="https://github.com/user-attachments/assets/2071c92e-2bbe-46f8-a338-05b0f53d381a" />
- Verification:
- User bob requests GET /api/resources/private/secret.txt.
- Server responds: 403 Forbidden. <img width="1193" height="721" alt="Screenshot_20260123_154446" src="https://github.com/user-attachments/assets/dd092a10-2f8c-4a3c-b48f-d540c483bb5a" />
- Exploit:
- User bob requests GET /api/resources//private/secret.txt.
- Server responds: 200 OK (Bypass successful). <img width="1193" height="721" alt="Screenshot_20260123_154544" src="https://github.com/user-attachments/assets/27ebb82c-f7c2-467d-ae82-f495ae3aa2d4" />
Impact
This vulnerability impacts the confidentiality and integrity of data stored in filebrowser.
- Confidentiality: Users can read files they are explicitly forbidden from accessing.
- Integrity: If the user has general write permissions but is restricted from specific directories via rules, they can bypass these restrictions to rename, delete, or modify files.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/filebrowser/filebrowser/v2 | all versions | 2.57.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/filebrowser/filebrowser/v2. 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 github.com/filebrowser/filebrowser/v2 to 2.57.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4mh3-h929-w968 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-4mh3-h929-w968 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-4mh3-h929-w968. 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-4mh3-h929-w968 in your dependencies?
O3 detects GHSA-4mh3-h929-w968 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.