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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

• CVE-2026-32178: 2.28% estimated exploitation activity in the next 30 days; percentile 83.15 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 <a name="affected-packages"</aAffected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below <a name=".NET 8"</a.NET 8 Package name | Affected version |…

Published by the source

14 Apr 2026, 23:27 UTC

Last modified by the source

14 Apr 2026, 23:27 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-vmwf-m9c5-3jvc

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# Patch Next advisory brief: CVE-2026-32178

Advisory: Microsoft Security Advisory CVE-2026-32178 – .NET Spoofing Vulnerability
IDs: CVE-2026-32178, GHSA-vmwf-m9c5-3jvc
Record: https://patchnext.com/advisories/cve-2026-32178 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.netcore.app.runtime.win-x86 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.win-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.linux-musl-x64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.linux-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.linux-arm 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.osx-x64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.linux-x64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.osx-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.linux-musl-arm 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.win-arm 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.linux-musl-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.netcore.app.runtime.win-x64 10.0.6, 9.0.15, 8.0.26. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.netcore.app.runtime.win-x86: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.win-arm64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.linux-arm64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.linux-arm: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.osx-x64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.linux-x64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.osx-arm64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.win-arm: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15
- NuGet microsoft.netcore.app.runtime.win-x64: affected >= 10.0.0, <= 10.0.5; >= 9.0.0, <= 9.0.14; >= 8.0.0, <= 8.0.25; fixed in 8.0.26, 10.0.6, 9.0.15

## Suggested inspection (read-only)
- NuGet microsoft.netcore.app.runtime.win-x86: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.osx-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.osx-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-x64: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on microsoft.netcore.app.runtime.win-x86, microsoft.netcore.app.runtime.win-arm64, microsoft.netcore.app.runtime.linux-musl-x64, microsoft.netcore.app.runtime.linux-arm64, microsoft.netcore.app.runtime.linux-arm, microsoft.netcore.app.runtime.osx-x64, microsoft.netcore.app.runtime.linux-x64, microsoft.netcore.app.runtime.osx-arm64, microsoft.netcore.app.runtime.linux-musl-arm, microsoft.netcore.app.runtime.win-arm, microsoft.netcore.app.runtime.linux-musl-arm64, microsoft.netcore.app.runtime.win-x64.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vmwf-m9c5-3jvc (GitHub-reviewed advisory GHSA-vmwf-m9c5-3jvc lists affected ranges: NuGet microsoft.netcore.app.runtime.linux-arm >=10.0.0 =9.0.0 =8.0.0 =10.0.0 =9.0.0 =8.0.0 =10.0.0 =9.0.0 =8.0.0 =10.0.0 =9.0.0 =8.0.0 <=8.0.25; NuGet…)

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