GHSA-j66f-h9hm-975m
MEDIUMGHSA-j66f-h9hm-975m is a medium-severity (CVSS 6.5) Unrestricted File Upload vulnerability in UmbracoCms. 3 public exploit references exist, so weaponization risk is real. O3 Security confirms whether GHSA-j66f-h9hm-975m is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Unrestricted Upload of File with Dangerous Type in Umbraco CMS
Real-World Exposure
UmbracoCmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Umbraco CMS 8.5.3 allows an authenticated file upload (and consequently Remote Code Execution) via the Install Package functionality.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | UmbracoCms | all versions | 8.5.4 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for UmbracoCms. 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 UmbracoCms to 8.5.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-j66f-h9hm-975m 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-j66f-h9hm-975m 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-j66f-h9hm-975m. 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-j66f-h9hm-975m in your dependencies?
O3 detects GHSA-j66f-h9hm-975m across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.