CVE-2025-48953
MEDIUMCVE-2025-48953 is a medium-severity (CVSS 5.5) Unrestricted File Upload vulnerability in Umbraco.Cms. O3 Security confirms whether CVE-2025-48953 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Umbraco Vulnerable to By-Pass of Configured Allowed Extensions for File Uploads
Blast Radius
Umbraco.CmsReal-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 is an ASP.NET content management system (CMS). Starting in version 14.0.0 and prior to versions 15.4.2 and 16.0.0, it's possible to upload a file that doesn't adhere with the configured allowable file extensions via a manipulated API request. The issue is patched in versions 15.4.2 and 16.0.0. No known workarounds are available.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Umbraco.Cms | ≥ 14.0.0&&< 15.4.2 | 15.4.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Umbraco.Cms. 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 Umbraco.Cms to 15.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-48953 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 CVE-2025-48953 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 CVE-2025-48953. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-48953 in your dependencies?
O3 detects CVE-2025-48953 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.