🛡️ CVE-2026-50659 — .net

🟡 CVSS 6.5 — Medium ✅ No Known Exploit CWE-116 NVD
6.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-x64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-x64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-arm64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-x64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x64) | >= 10.0.0, <= 10.0.9 | 10.0.10

[Microsoft.NetCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x86) | >= 10.0.0, <= 10.0.9 | 10.0.10

<a name=".NET 9.0"></a>.NET 9.0

Package name | Affected version | Patched version

------------ | ---------------- | -------------------------

[Microsoft.NetCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-x64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-x64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-arm64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-x64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm64) | >= 9.0.0, <= 9.0.17 | 9.0.18

[Microsoft.NetCore.App.Runtime.win-x64](https://w

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity high, availability none.

Weakness class

CVE-2026-50659 is classified as CWE-116: Improper Encoding or Escaping of Output. Output is emitted without encoding it for the context it lands in, so data is interpreted as markup or code.

Affected software

CVE-2026-50659 is recorded against 18 packages.

  • .net (from 10.0.0 up to 10.0.6)
  • .net-framework
  • dotnet
  • dotnet-sdk
  • microsoft.netcore.app.runtime.linux-arm (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.linux-arm64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.linux-musl-arm (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.linux-musl-arm64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.linux-musl-x64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.linux-x64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.osx-arm64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.osx-x64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.win-arm (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.win-arm64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.win-x64 (from 8.0.0 up to 8.0.29)
  • microsoft.netcore.app.runtime.win-x86 (from 8.0.0 up to 8.0.29)
  • visual-studio-2022 (from 17.14.0 up to 17.14.36)
  • visual-studio-2026 (from 18.7.0 up to 18.7.4)

Timeline and source

Published on 14 July 2026 and last revised on 24 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

msrc.microsoft.com

Details

Severity MEDIUM
CVSS Score 6.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
CWE CWE-116
Public Exploit ✅ No
Source NVD
Published 2026-07-14
Updated 2026-08-12
Modified 2026-07-24

Affected Packages

Software From version Fixed in
.net 10.0.0 10.0.6
.net-framework — —
dotnet — —
dotnet-sdk — —
microsoft.netcore.app.runtime.linux-arm 8.0.0 8.0.29
microsoft.netcore.app.runtime.linux-arm64 8.0.0 8.0.29
microsoft.netcore.app.runtime.linux-musl-arm 8.0.0 8.0.29
microsoft.netcore.app.runtime.linux-musl-arm64 8.0.0 8.0.29
microsoft.netcore.app.runtime.linux-musl-x64 8.0.0 8.0.29
microsoft.netcore.app.runtime.linux-x64 8.0.0 8.0.29
microsoft.netcore.app.runtime.osx-arm64 8.0.0 8.0.29
microsoft.netcore.app.runtime.osx-x64 8.0.0 8.0.29
microsoft.netcore.app.runtime.win-arm 8.0.0 8.0.29
microsoft.netcore.app.runtime.win-arm64 8.0.0 8.0.29
microsoft.netcore.app.runtime.win-x64 8.0.0 8.0.29
microsoft.netcore.app.runtime.win-x86 8.0.0 8.0.29
visual-studio-2022 17.14.0 17.14.36
visual-studio-2026 18.7.0 18.7.4

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