CVE-2025-21171
HIGHCVE-2025-21171 is a high-severity (CVSS 7.5) CWE-122 vulnerability in Microsoft.NetCore.App.Runtime.linux-arm. O3 Security confirms whether CVE-2025-21171 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Microsoft Security Advisory CVE-2025-21171 | .NET Remote Code Execution Vulnerability
Real-World Exposure
Microsoft.NetCore.App.Runtime.linux-arm.NETMicrosoft.NetCore.App.Runtime.linux-arm64.NETMicrosoft.NetCore.App.Runtime.linux-musl-arm.NETMicrosoft.NetCore.App.Runtime.linux-musl-arm64.NETMicrosoft.NetCore.App.Runtime.linux-musl-x64.NETMicrosoft.NetCore.App.Runtime.linux-x64.NETMicrosoft.NetCore.App.Runtime.osx-arm64.NETMicrosoft.NetCore.App.Runtime.osx-x64+4 moreReal-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
.NET Remote Code Execution Vulnerability
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Microsoft.NetCore.App.Runtime.linux-arm | ≥ 9.0.0&&< 9.0.1 | 9.0.1 |
| .NETNuGet | Microsoft.NetCore.App.Runtime.linux-arm64 | ≥ 9.0.0&&< 9.0.1 | 9.0.1 |
| .NETNuGet | Microsoft.NetCore.App.Runtime.linux-musl-arm | ≥ 9.0.0&&< 9.0.1 | 9.0.1 |
| .NETNuGet | Microsoft.NetCore.App.Runtime.linux-musl-arm64 | ≥ 9.0.0&&< 9.0.1 | 9.0.1 |
| .NETNuGet | Microsoft.NetCore.App.Runtime.linux-musl-x64 | ≥ 9.0.0&&< 9.0.1 | 9.0.1 |
| .NETNuGet | Microsoft.NetCore.App.Runtime.linux-x64 | ≥ 9.0.0&&< 9.0.1 | 9.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.NetCore.App.Runtime.linux-arm. 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 Microsoft.NetCore.App.Runtime.linux-arm to 9.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-21171 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-2025-21171 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-2025-21171. 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-2025-21171 in your dependencies?
O3 detects CVE-2025-21171 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.