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Microsoft Security Advisory CVE-2026-32178 – .NET Spoofing Vulnerability

Low severity GitHub Reviewed Published Apr 14, 2026 in dotnet/runtime • Updated Apr 14, 2026

Package

nuget Microsoft.NetCore.App.Runtime.linux-arm (NuGet)

Affected versions

>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25

Patched versions

10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.linux-musl-x64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.linux-x64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.osx-x64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.win-arm (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.win-arm64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.win-x64 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26
nuget Microsoft.NetCore.App.Runtime.win-x86 (NuGet)
>= 10.0.0, <= 10.0.5
>= 9.0.0, <= 9.0.14
>= 8.0.0, <= 8.0.25
10.0.6
9.0.15
8.0.26

Description

Executive Summary:

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 8.0, .NET 9.0, and .NET 10.0. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

A vulnerability exists in System.Net.Mail where specially crafted data allows an unauthorized attacker to perform a spoofing attack over the network.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/12345

CVSS Details

  • Version: 3.1
  • Severity: High
  • Score: 7.5
  • Vector: 7.5: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
  • Weakness: CWE-138: Improper Neutralization of Special Elements

Affected Platforms

  • Platforms: All
  • Architectures: All

Affected Packages

The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below

.NET 8

Package name Affected version Patched version
Microsoft.NetCore.App.Runtime.linux-arm >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.linux-arm64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.linux-musl-arm >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.linux-musl-arm64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.linux-musl-x64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.linux-x64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.osx-arm64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.osx-x64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.win-arm >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.win-arm64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.win-x64 >= 8.0.0, <= 8.0.25 8.0.26
Microsoft.NetCore.App.Runtime.win-x86 >= 8.0.0, <= 8.0.25 8.0.26

.NET 9

Package name Affected version Patched version
Microsoft.NetCore.App.Runtime.linux-arm >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.linux-arm64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.linux-musl-arm >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.linux-musl-arm64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.linux-musl-x64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.linux-x64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.osx-arm64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.osx-x64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.win-arm >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.win-arm64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.win-x64 >= 9.0.0, <= 9.0.14 9.0.15
Microsoft.NetCore.App.Runtime.win-x86 >= 9.0.0, <= 9.0.14 9.0.15

.NET 10

Package name Affected version Patched version
Microsoft.NetCore.App.Runtime.linux-arm >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.linux-arm64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.linux-musl-arm >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.linux-musl-arm64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.linux-musl-x64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.linux-x64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.osx-arm64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.osx-x64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.win-arm >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.win-arm64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.win-x64 >= 10.0.0, <= 10.0.5 10.0.6
Microsoft.NetCore.App.Runtime.win-x86 >= 10.0.0, <= 10.0.5 10.0.6

Advisory FAQ

How do I know if I am affected?

If using a package listed in affected packages, you're exposed to the vulnerability.

How do I fix the issue?

  1. To fix the issue please install the latest version of .NET 8.0, NET 9.0, or .NET 10.0, as appropriate. 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.
  2. If your application references the vulnerable package, update the package reference to the patched version. You can list the versions you have installed by running the dotnet --info command.

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

CVE-2026-32178

Acknowledgements

Ludvig Pedersen

Revisions

V1.0 (April 14, 2026): Advisory published.

References

@bribrothers bribrothers published to dotnet/runtime Apr 14, 2026
Published by the National Vulnerability Database Apr 14, 2026
Published to the GitHub Advisory Database Apr 14, 2026
Reviewed Apr 14, 2026
Last updated Apr 14, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N

EPSS score

Weaknesses

Improper Neutralization of Special Elements

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as control elements or syntactic markers when they are sent to a downstream component. Learn more on MITRE.

CVE ID

CVE-2026-32178

GHSA ID

GHSA-vmwf-m9c5-3jvc

Source code

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