GHSA-74jp-vm22-8q8x: Microsoft Security Advisory CVE-2026-50659 – .NET Spoofing Vulnerability

Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in .NET SMTP client (System.Net.Mail). This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. A spoofing vulnerability exists in the SMTP client implementation (System.Net.Mail) in .NET 8, .NET 9, and .NET 10, where an attacker can spoof messages during message routing. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/TBD CVSS Details - Version: 3.1 - Severity: Medium - Score: 6.5 - Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N - Weakness: CWE-116 (Improper Encoding or Escaping of Output) Affected Platforms - Platforms: All - Architectures: All <a name="affected-packages"></a>Affected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below <a name=".NET 10.0"></a>.NET 10.0 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.NetCore.App.Runtime.linux-arm | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.linux-arm64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.linux-musl-arm | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.linux-musl-arm64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.linux-musl-x64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.linux-x64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.osx-arm64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.osx-x64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.win-arm | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.win-arm64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.win-x64 | >= 10.0.0, <= 10.0.9 | 10.0.10 Microsoft.NetCore.App.Runtime.win-x86 | >= 10.0.0, <= 10.0.9 | 10.0.10 <a name="