GHSA-rh58-r7jh-xhx3 — Microsoft.NETCore.App.Run…
HIGHGHSA-rh58-r7jh-xhx3 is a high-severity (CVSS 7.5) vulnerability in Microsoft.NETCore.App.Runtime.win-x86. A fix is available for Microsoft.NETCore.App.Runtime.win-x86 — see the affected versions and patch details below.
.NET Core Elevation of Privilege Vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-rh58-r7jh-xhx3.
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.
How urgent is this, really
GHSA-rh58-r7jh-xhx3 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,238 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
Microsoft.NETCore.App.Runtime.win-x86.NETMicrosoft.NETCore.App.Runtime.win-x86.NETMicrosoft.NETCore.App.Runtime.win-x64.NETMicrosoft.NETCore.App.Runtime.win-x64.NETMicrosoft.NETCore.App.Runtime.win-arm64.NETMicrosoft.NETCore.App.Runtime.win-arm64.NETMicrosoft.NETCore.App.Runtime.win-arm.NETMicrosoft.NETCore.App.Runtime.win-arm+25 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
Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 5.0 and .NET Core 3.1. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.
A denial of service vulnerability exists in .NET 5.0, .NET Core 3.1 and .NET Core 2.1 where .NET (Core) server applications providing WebSocket endpoints could be tricked into endlessly looping while trying to read a single WebSocket frame.
Patches
-
If you're using .NET 5.0, you should download and install Runtime 5.0.9 or SDK 5.0.206 (for Visual Studio 2019 v16.8) or SDK 5.0.303 (for Visual Studio 2019 V16.10) from https://dotnet.microsoft.com/download/dotnet-core/5.0.
-
If you're using .NET Core 3.1, you should download and install Runtime 3.1.18 or SDK 3.1.118 (for Visual Studio 2019 v16.4) or 3.1.412 (for Visual Studio 2019 v16.7 or later) from https://dotnet.microsoft.com/download/dotnet-core/3.1.
-
If you're using .NET Core 2.1, you should download and install Runtime 2.1.29 or SDK 2.1.525 (for Visual Studio 2019 v15.9) or 2.1.817 from https://dotnet.microsoft.com/download/dotnet-core/2.1.
Other Details
- Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/194
- An Issue for this can be found at https://github.com/dotnet/runtime/issues/57175
- MSRC details for this can be found at https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-26423
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Microsoft.NETCore.App.Runtime.win-x86 | ≥ 3.1.0&&< 3.1.18 | 3.1.18dotnet add package Microsoft.NETCore.App.Runtime.win-x86 --version 3.1.18 |
| .NETNuGet | Microsoft.NETCore.App.Runtime.win-x86 | ≥ 5.0.0&&< 5.0.9 | 5.0.9dotnet add package Microsoft.NETCore.App.Runtime.win-x86 --version 5.0.9 |
| .NETNuGet | Microsoft.NETCore.App.Runtime.win-x64 | ≥ 3.1.0&&< 3.1.18 | 3.1.18dotnet add package Microsoft.NETCore.App.Runtime.win-x64 --version 3.1.18 |
| .NETNuGet | Microsoft.NETCore.App.Runtime.win-x64 | ≥ 5.0.0&&< 5.0.9 | 5.0.9dotnet add package Microsoft.NETCore.App.Runtime.win-x64 --version 5.0.9 |
| .NETNuGet | Microsoft.NETCore.App.Runtime.win-arm64 | ≥ 3.1.0&&< 3.1.18 | 3.1.18dotnet add package Microsoft.NETCore.App.Runtime.win-arm64 --version 3.1.18 |
| .NETNuGet | Microsoft.NETCore.App.Runtime.win-arm64 | ≥ 5.0.0&&< 5.0.9 | 5.0.9dotnet add package Microsoft.NETCore.App.Runtime.win-arm64 --version 5.0.9 |
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.win-x86, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Microsoft.NETCore.App.Runtime.win-x86 to 3.1.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rh58-r7jh-xhx3 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-rh58-r7jh-xhx3 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-rh58-r7jh-xhx3. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| .NET Core on Red Hat Enterprise Linux | rh-dotnet31-dotnet-0:3.1.118-1.el7_9 | RHSA-2021:3143 |
| .NET Core on Red Hat Enterprise Linux | rh-dotnet50-dotnet-0:5.0.206-1.el7_9 | RHSA-2021:3147 |
| Red Hat Enterprise Linux 8 | dotnet3.1-0:3.1.118-1.el8_4 | RHSA-2021:3142 |
| Red Hat Enterprise Linux 8 | dotnet5.0-0:5.0.206-1.el8_4 | RHSA-2021:3148 |
Frequently Asked Questions
Is GHSA-rh58-r7jh-xhx3 in your dependencies?
O3 Security finds GHSA-rh58-r7jh-xhx3 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.