.NET Spoofing Vulnerability
Priority MEDIUM 41CWE-166Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Spoofing
- Confidentiality · integrity · availability
- None · High · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Microsoft. Impact type from Microsoft.
Summary
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00997 62nd percentileScored 2026-11-07
Fix Fixed System.Security.Cryptography.Cose (NuGet): 8.0.2, 9.0.13, 10.0.3Microsoft: 3 updates
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Microsoft | .NET 10.0 | 10.0.0 to before 10.0.3 | 10.0.3 | Patch available | CNA |
| Microsoft | .NET 8.0 | 8.0.0 to before 8.0.24 | 8.0.24 | Patch available | CNA |
| Microsoft | .NET 9.0 | 9.0.0 to before 9.0.13 | 9.0.13 | Patch available | CNA |
| — | System.Security.Cryptography.Cose (NuGet) | 8.0.0 to before 8.0.2 | 8.0.2 | Patch available | GHSA-qvhc-9v3j-5rfw |
| — | System.Security.Cryptography.Cose (NuGet) | 9.0.0 to before 9.0.13 | 9.0.13 | Patch available | GHSA-qvhc-9v3j-5rfw |
| — | System.Security.Cryptography.Cose (NuGet) | 10.0.0 to before 10.0.3 | 10.0.3 | Patch available | GHSA-qvhc-9v3j-5rfw |
- .NET 10.0 VendorMicrosoft Affected 10.0.0 to before 10.0.3 Fixed in 10.0.3 Patch available CNA
- .NET 8.0 VendorMicrosoft Affected 8.0.0 to before 8.0.24 Fixed in 8.0.24 Patch available CNA
- .NET 9.0 VendorMicrosoft Affected 9.0.0 to before 9.0.13 Fixed in 9.0.13 Patch available CNA
- System.Security.Cryptography.Cose (NuGet) Vendor— Affected 8.0.0 to before 8.0.2 Fixed in 8.0.2 Patch available GHSA-qvhc-9v3j-5rfw
- System.Security.Cryptography.Cose (NuGet) Vendor— Affected 9.0.0 to before 9.0.13 Fixed in 9.0.13 Patch available GHSA-qvhc-9v3j-5rfw
- System.Security.Cryptography.Cose (NuGet) Vendor— Affected 10.0.0 to before 10.0.3 Fixed in 10.0.3 Patch available GHSA-qvhc-9v3j-5rfw
CPE configurations NVD · 4
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:microsoft:.net:*:*:*:*:*:*:*:* | 8.0.0 to before 8.0.24; 9.0.0 to before 9.0.13; 10.0.0 to before 10.0.3 | Vulnerable | Microsoft |
| cpe:2.3:o:apple:macos:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Apple |
| cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Linux |
| cpe:2.3:o:microsoft:windows:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Microsoft |
- cpe:2.3:a:microsoft:.net:*:*:*:*:*:*:*:* Versions 8.0.0 to before 8.0.24; 9.0.0 to before 9.0.13; 10.0.0 to before 10.0.3 Vulnerable ·Microsoft
- cpe:2.3:o:apple:macos:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Apple
- cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Linux
- cpe:2.3:o:microsoft:windows:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Microsoft
Remediation
- Fix · GHSA-qvhc-9v3j-5rfw System.Security.Cryptography.Cose (NuGet) Fixed in 8.0.2 Advisory →
- Fix · GHSA-qvhc-9v3j-5rfw System.Security.Cryptography.Cose (NuGet) Fixed in 9.0.13 Advisory →
- Fix · GHSA-qvhc-9v3j-5rfw System.Security.Cryptography.Cose (NuGet) Fixed in 10.0.3 Advisory →
Microsoft 3 updates
- Security Update
- .NET 9.0 installed on Linux 9.0.13
- .NET 9.0 installed on Mac OS 9.0.13
- .NET 9.0 installed on Windows 9.0.13
- Security Update
- .NET 8.0 installed on Linux 8.0.24
- .NET 8.0 installed on Mac OS 8.0.24
- .NET 8.0 installed on Windows 8.0.24
- Security Update
- .NET 10.0 installed on Linux 10.0.3
- .NET 10.0 installed on Mac OS 10.0.3
- .NET 10.0 installed on Windows 10.0.3
Vendor assessments
Microsoft
Microsoft's page for this CVE →
- Impact
- Spoofing
- Exploited
- No
- Publicly disclosed
- No
- Exploitability
- Exploitation Unlikely
Timeline
- 2026-10-02 Threatist record created from CVE-2026-21218
- 2026-10-03 Alias added: GHSA-qvhc-9v3j-5rfw
References
More Microsoft .net vulnerabilities
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- TI-2023-19596 .NET and Visual Studio Denial of Service Vulnerability KEVCVSS 3.1HIGH 7.5
- TI-2023-19588 Microsoft QUIC Denial of Service Vulnerability CVSS 3.1HIGH 7.5
- TI-2024-14152 .NET and Visual Studio Denial of Service Vulnerability CVSS 3.1HIGH 7.5
- TI-2021-08380 .NET Core Remote Code Execution Vulnerability CVSS 3.1CRITICAL 9.8
Sources
- CVE-2026-21218 · CVE Program
- CVE-2026-21218 · NVD
- FIRST EPSS
- GHSA-qvhc-9v3j-5rfw · GitHub Advisory Database · CC BY 4.0
- CVE-2026-21218 · Microsoft Security Update Guide
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences