CVE-2026-21218 .NET Spoofing Vulnerability
An attacker can perform network spoofing due to improper handling of missing special elements in the .NET runtime.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-21218?
CVE-2026-21218 is a high-severity vulnerability in Microsoft .Net, published on 10 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
Weakness: CWE-166
Which versions are affected by CVE-2026-21218?
8 open source packages ship an affected version, including System.Security.Cryptography.Cose, dotnet and dotnet-sdk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
System.Security.Cryptography.Cose NuGet | From 10.0.0 | 10.0.3 |
System.Security.Cryptography.Cose NuGet | From 10.0.0 | 10.0.3 |
System.Security.Cryptography.Cose NuGet | From 8.0.0 | 8.0.2 |
System.Security.Cryptography.Cose NuGet | From 8.0.0 | 8.0.2 |
System.Security.Cryptography.Cose NuGet | From 9.0.0 | 9.0.13 |
System.Security.Cryptography.Cose NuGet | From 9.0.0 | 9.0.13 |
2 more packages
dotnet Bitnami | From 8.0.0 | 8.0.24, 9.0.13, 10.0.3 |
dotnet-sdk Bitnami | From 8.0.0 | 8.0.24, 9.0.13, 10.0.3 |
Products include Microsoft .Net.
How do I fix CVE-2026-21218?
Upgrade System.Security.Cryptography.Cose to a fixed version for your release line: 10.0.3, 8.0.2 or 9.0.13.
Is CVE-2026-21218 being exploited?
There is no known exploitation of CVE-2026-21218 in the wild and no public exploit code.
Other vulnerabilities in Microsoft .Net
- CVE-2024-43498 .NET and Visual Studio Remote Code Execution Vulnerability
- CVE-2024-0057 NET, .NET Framework, and Visual Studio Security Feature Bypass Vulnerability
- CVE-2026-96957 .NET Security Feature Bypass Vulnerability
- CVE-2026-69439 .NET and Visual Studio Elevation of Privilege Vulnerability
- CVE-2026-71328 .NET and Visual Studio Remote Code Execution Vulnerability
Sources
Also known as BELL-CVE-2026-21218, BIT-dotnet-2026-21218, BIT-dotnet-sdk-2026-21218, GHSA-qvhc-9v3j-5rfw, MINI-6wgc-8xfm-5x6v, MINI-jpv7-469r-894p and 3 more.