CVE-2026-50659: .NET Spoofing Vulnerability

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-14 · updated 2026-11-01
Weakness: CWE-116

Description

Improper encoding or escaping of output in .NET allows an authorized attacker to perform spoofing over a network.

Affected products

Microsoft .NET: from 8.0.0 before 8.0.29; from 9.0.0 before 9.0.18; from 10.0.0 before 10.0.6 — fixed in 8.0.29, 9.0.18, 10.0.6
Microsoft .NET Framework: 3.5; 4.8.1, 4.8, 4.6.2, 4.7, 4.7.1, 4.7.2 (and their updates)
Microsoft Visual Studio 2022 version 17.14: from 17.12.0 before 17.12.22; from 17.14.0 before 17.14.36 — fixed in 17.12.22, 17.14.36
Microsoft Visual Studio 2026 version 18.9: from 18.7.0 before 18.7.4 — fixed in 18.7.4
Microsoft .NET 10.0 runtime: from 10.0.0 before 10.0.10 — fixed in 10.0.10
Microsoft .NET 8.0 runtime: from 8.0.0 before 8.0.29 — fixed in 8.0.29
Microsoft .NET 9.0 runtime: from 9.0.0 before 9.0.18 — fixed in 9.0.18
Microsoft .NET Framework 3.5: from 3.5.0 before 2.0.50727.8983 & 3.0.30729.8978 — fixed in 2.0.50727.8983 & 3.0.30729.8978
Microsoft .NET Framework 3.5 AND 4.7.2: from 4.7.0 before 2.0.50727.9069 & 3.0.30729.9067 & 4.7.4143.0 — fixed in 2.0.50727.9069 & 3.0.30729.9067 & 4.7.4143.0
Microsoft .NET Framework 3.5 AND 4.8: from 4.8.0 before 2.0.50727.9069 & 3.0.30729.9067 & 4.8.4803.0 — fixed in 2.0.50727.9069 & 3.0.30729.9067 & 4.8.4803.0
Microsoft .NET Framework 3.5 AND 4.8.1: from 4.8.1 before 2.0.50727.9182 & 3.0.30729.9168 & 4.8.9339.0 — fixed in 2.0.50727.9182 & 3.0.30729.9168 & 4.8.9339.0
Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2: from 4.7.0 before 4.7.4143.0 — fixed in 4.7.4143.0
Microsoft .NET Framework 4.8: from 4.8.0 before 4.8.4803.0 — fixed in 4.8.4803.0
Microsoft .NET Framework 4.8.1: from 4.8.0.0 before 4.8.9340.0 — fixed in 4.8.9340.0
Microsoft Visual Studio 2026 version 18.7: from 18.0 before 18.7.4 — fixed in 18.7.4
Microsoft Visual Studio 2022 version 17.14: from 17.12.0 before 17.12.22 — fixed in 17.12.22

How to fix

Upgrade to a fixed version: Microsoft .NET 8.0.29, 9.0.18, 10.0.6; Microsoft Visual Studio 2022 version 17.14 17.12.22, 17.14.36; Microsoft Visual Studio 2026 version 18.9 18.7.4; Microsoft .NET 10.0 runtime 10.0.10; Microsoft .NET 8.0 runtime 8.0.29; Microsoft .NET 9.0 runtime 9.0.18; Microsoft .NET Framework 3.5 2.0.50727.8983 & 3.0.30729.8978; Microsoft .NET Framework 3.5 AND 4.7.2 2.0.50727.9069 & 3.0.30729.9067 & 4.7.4143.0; Microsoft .NET Framework 3.5 AND 4.8 2.0.50727.9069 & 3.0.30729.9067 & 4.8.4803.0; Microsoft .NET Framework 3.5 AND 4.8.1 2.0.50727.9182 & 3.0.30729.9168 & 4.8.9339.0; Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2 4.7.4143.0; Microsoft .NET Framework 4.8 4.8.4803.0. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50659

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