Improper Encoding or Escaping of Output in Microsoft products - CVE-2026-50659

Vulnerability identifier: #VU138088

CSH Severity: Low

CVSS v4: 5.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-50659

CWE-ID: CWE-116

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote user to perform spoofing.

The vulnerability exists due to improper encoding or escaping of output in .NET for macOS when handling network requests. A remote user can send crafted input to perform spoofing.

.NET
.NET for Linux
.NET for macOS
Visual Studio
Red Hat CodeReady Linux Builder for IBM z Systems - Extended Update Support
Red Hat CodeReady Linux Builder for ARM 64 - Extended Update Support
Red Hat CodeReady Linux Builder for Power, little endian - Extended Update Support
Red Hat CodeReady Linux Builder for x86_64 - Extended Update Support
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Ubuntu
dotnet10 (Ubuntu package)
dotnet8.0 (Red Hat package)
dotnet9.0 (Red Hat package)

Install security update from vendor's website.

.NET - addressed in versions 8.0.29, 9.0.18
.NET for Linux - addressed in versions 8.0.29, 9.0.18
.NET for macOS - addressed in versions 8.0.29, 9.0.18
Visual Studio - update to 17.12.22
dotnet10 (Ubuntu package) - addressed in versions 8.0.29-0ubuntu1~22.04.1, 8.0.29-0ubuntu1~24.04.1, 8.0.129-0ubuntu1~22.04.1, 8.0.129-0ubuntu1~24.04.1, 8.0.129-8.0.29-0ubuntu1~22.04.1, 8.0.129-8.0.29-0ubuntu1~24.04.1, 10.0.10-0ubuntu1~24.04.1, 10.0.10-0ubuntu1~26.04.1, 10.0.110-0ubuntu1~24.04.1, 10.0.110-0ubuntu1~26.04.1, 10.0.110-10.0.10-0ubuntu1~24.04.1, 10.0.110-10.0.10-0ubuntu1~26.04.1
dotnet8.0 (Red Hat package) - update to 8.0.130-1.el10_0
dotnet9.0 (Red Hat package) - update to 9.0.120-1.el10_0

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2026-50659

• Multiple vulnerabilities in Visual Studio
• Ubuntu update for dotnet10
• Red Hat Enterprise Linux 10 update for .NET 8.0
• Red Hat Enterprise Linux 10 update for .NET 9.0