How severe is CVE-2021-26423?

CVE-2021-26423 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-26423?

CVE-2021-26423 affects the following packages: Microsoft.NETCore.App.Runtime.win-x86 (NuGet), Microsoft.NETCore.App.Runtime.win-x86 (NuGet), Microsoft.NETCore.App.Runtime.win-x64 (NuGet), Microsoft.NETCore.App.Runtime.win-x64 (NuGet), Microsoft.NETCore.App.Runtime.win-arm64 (NuGet), Microsoft.NETCore.App.Runtime.win-arm64 (NuGet), Microsoft.NETCore.App.Runtime.win-arm (NuGet), Microsoft.NETCore.App.Runtime.win-arm (NuGet), and 25 more. Ecosystems affected: NuGet.

How do I fix CVE-2021-26423?

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 CVE-2021-26423 is resolved across your whole dependency graph.

How do I detect CVE-2021-26423 in my NuGet dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.NETCore.App.Runtime.win-x86. 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.

How do I mitigate CVE-2021-26423 if there is no patch (or I can't update yet)?

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 does O3 Security protect against CVE-2021-26423?

O3 pinpoints whether CVE-2021-26423 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2021-26423 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-26423 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-26423?

CVE-2021-26423 has an EPSS (Exploit Prediction Scoring System) score of 3.7%, placing it in the 88th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2021-26423 published, and has it been updated?

CVE-2021-26423 was published on August 12, 2021 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET NuGet

CVE-2021-26423

HIGH

.NET Core Elevation of Privilege Vulnerability

Also known asBIT-dotnet-2021-26423BIT-dotnet-sdk-2021-26423GHSA-rh58-r7jh-xhx3

Published

Aug 12, 2021

Updated

Apr 10, 2026

Affected

33 pkgs

Patched

33 / 33

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

3.7%probability of exploitation in next 30 days

Lower Risk88th percentile+0.37%

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

33 pkgs affected

.NETMicrosoft.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 more

Real-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 Core and Visual Studio Denial of Service Vulnerability

Affected Packages

33 total 33 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`Microsoft.NETCore.App.Runtime.win-x86`	≥ 3.1.0&&< 3.1.18	3.1.18
.NETNuGet	`Microsoft.NETCore.App.Runtime.win-x86`	≥ 5.0.0&&< 5.0.9	5.0.9
.NETNuGet	`Microsoft.NETCore.App.Runtime.win-x64`	≥ 3.1.0&&< 3.1.18	3.1.18
.NETNuGet	`Microsoft.NETCore.App.Runtime.win-x64`	≥ 5.0.0&&< 5.0.9	5.0.9
.NETNuGet	`Microsoft.NETCore.App.Runtime.win-arm64`	≥ 3.1.0&&< 3.1.18	3.1.18
.NETNuGet	`Microsoft.NETCore.App.Runtime.win-arm64`	≥ 5.0.0&&< 5.0.9	5.0.9

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.NETCore.App.Runtime.win-x86. 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.win-x86 to 3.1.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-26423 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-2021-26423 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-2021-26423. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

.NET Core and Visual Studio Denial of Service Vulnerability

O3 Security · Impact-Aware SCA

Is CVE-2021-26423 in your dependencies?

O3 detects CVE-2021-26423 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works