GHSA-74jp-vm22-8q8x BIT-dotnet-2026-50659 BIT-dotnet-sdk-2026-50659 CVE-2026-50659
Microsoft Security Advisory CVE-2026-50659 – .NET Spoofing Vulnerability
- Severity
- 6.5 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.74%
- Chance of exploitation in the next 30 days. Higher than 54.54% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-116 Improper Encoding or Escaping of Output
- Fix
- Available
- 12 packages have a fixed version
Description
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=".NET 9.0"></a>.NET 9.0
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.NetCore.App.Runtime.linux-arm | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.linux-arm64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.linux-musl-arm | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.linux-musl-arm64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.linux-musl-x64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.linux-x64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.osx-arm64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.osx-x64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.win-arm | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.win-arm64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.win-x64 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
| Microsoft.NetCore.App.Runtime.win-x86 | >= 9.0.0, <= 9.0.17 | 9.0.18 |
<a name=".NET 8.0"></a>.NET 8.0
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.NetCore.App.Runtime.linux-arm | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.linux-arm64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.linux-musl-arm | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.linux-musl-arm64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.linux-musl-x64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.linux-x64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.osx-arm64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.osx-x64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.win-arm | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.win-arm64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.win-x64 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
| Microsoft.NetCore.App.Runtime.win-x86 | >= 8.0.0, <= 8.0.28 | 8.0.29 |
Advisory FAQ
<a name="how-affected"></a>How do I know if I am affected?
If using a package listed in affected packages, you're exposed to the vulnerability.
<a name="how-fix"></a>How do I fix the issue?
- To fix the issue please install the latest version of .NET. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, which will also update your .NET SDKs.
- If your application references the vulnerable nuget package, update the package reference to the patched version. You can list the versions you have installed by running the
dotnet --infocommand.
Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.
Additionally, if you've deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.
Other Information
Reporting Security Issues
If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.
Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.
Support
You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.
Disclaimer
The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
External Links
Acknowledgements
hamayanhamayan
Revisions
V1.0 (July 14, 2026): Advisory published.
Affected versions
NuGet
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
Microsoft.NetCore.App.Runtime.linux-arm NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.linux-arm --version 10.0.10
Microsoft.NetCore.App.Runtime.linux-arm64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.linux-arm64 --version 10.0.10
Microsoft.NetCore.App.Runtime.linux-musl-arm NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-arm --version 10.0.10
Microsoft.NetCore.App.Runtime.linux-musl-arm64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-arm64 --version 10.0.10
Microsoft.NetCore.App.Runtime.linux-musl-x64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-x64 --version 10.0.10
Microsoft.NetCore.App.Runtime.linux-x64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.linux-x64 --version 10.0.10
Microsoft.NetCore.App.Runtime.osx-arm64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.osx-arm64 --version 10.0.10
Microsoft.NetCore.App.Runtime.osx-x64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.osx-x64 --version 10.0.10
Microsoft.NetCore.App.Runtime.win-arm NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.win-arm --version 10.0.10
Microsoft.NetCore.App.Runtime.win-arm64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.win-arm64 --version 10.0.10
Microsoft.NetCore.App.Runtime.win-x64 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.win-x64 --version 10.0.10
Microsoft.NetCore.App.Runtime.win-x86 NuGet → 10.0.10
- dotnet
dotnet add package Microsoft.NetCore.App.Runtime.win-x86 --version 10.0.10
Severity breakdown
CVSS 3.1 6.5
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
Weakness
CWE-116: Improper Encoding or Escaping of Output
The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.
How to prevent it
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error. Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
- Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated. For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
- Architecture and Design, Implementation: Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.
- Architecture and Design: In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict allowlist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input.
- Architecture and Design: Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
- Requirements: Fully specify which encodings are required by components that will be communicating with each other.
- Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| CVE-2020-1147 .NET Framework, SharePoint Server, and Visual Studio Remote Code Execution Vulnerability | High Known exploited | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
| GHSA-87vj-4hqv-22p9 Microsoft Security Advisory CVE-2026-96233 - .NET and Visual Studio Denial of Service Vulnerability | High | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
| GHSA-2j93-m82w-73j2 Microsoft Security Advisory CVE-2026-96231 - .NET and Visual Studio Elevation of Privilege Vulnerability | High | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
| GHSA-w6wh-p4g7-mpj2 Microsoft Security Advisory CVE-2026-96225 - .NET and Visual Studio Elevation of Privilege Vulnerability | High | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
| GHSA-4mpw-cpwj-hxxj Microsoft Security Advisory CVE-2026-70197 - .NET and Visual Studio Remote Code Execution Vulnerability | High | Also affects Microsoft.NETCore.App.Runtime.win-arm64 |
| GHSA-fqpq-cx42-9jmm Microsoft Security Advisory CVE-2026-70194 - .NET and Visual Studio Security Feature Bypass Vulnerability | Medium | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
| GHSA-3rxq-g8rj-r2cf Microsoft Security Advisory CVE-2026-69651 - .NET and Visual Studio Denial of Service Vulnerability | High | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
| GHSA-wxxw-5cvc-53j7 Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability | Medium | Also affects Microsoft.NETCore.App.Runtime.linux-arm |
MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.
Check your repos with MergeHarbor