Microsoft Security Advisory CVE-2025-21171 | .NET Remote Code Execution Vulnerability

Exploitation

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

CVSS

8.1 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2025-21171: 1.72% estimated exploitation activity in the next 30 days; percentile 77.52 (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.

Microsoft Security Advisory CVE-2025-21171 | .NET Remote Code Execution Vulnerability <a name="executive-summary"</aExecutive summary Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 9.0. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. An attacker could exploit this vulnerability by sending a specially crafted request to the vulnerable web server. Announcement Announcement for this issue can be found at https://github.com/dotnet/runtime/issues/111423 <a name="mitigation-factors"</aMitigation factors Microsoft has not identified any mitigating factors for this vulnerability. <a name="affected-software"</aAffected software Any .NET 9.0 application running on .NET 9.0.0 or earlier. <a name="affected-packages"</aAffected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected packages versions listed below <a name=".NET 9"</a.NET 9…

Published by the source

14 Jan 2025, 19:43 UTC

Last modified by the source

14 Jan 2025, 19:43 UTC

Source last checked

26 Oct 2026, 17:03 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-p54p-p3qm-8vgj

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# Patch Next advisory brief: CVE-2025-21171

Advisory: Microsoft Security Advisory CVE-2025-21171 | .NET Remote Code Execution Vulnerability
IDs: CVE-2025-21171, GHSA-p54p-p3qm-8vgj
Record: https://patchnext.com/advisories/cve-2025-21171 (revision 1, source checked 26 Oct 2026, 17:03 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
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 9.0.1; microsoft.netcore.app.runtime.win-arm64 9.0.1; microsoft.netcore.app.runtime.linux-musl-x64 9.0.1; microsoft.netcore.app.runtime.linux-arm64 9.0.1; microsoft.netcore.app.runtime.linux-arm 9.0.1; microsoft.netcore.app.runtime.osx-x64 9.0.1; microsoft.netcore.app.runtime.linux-x64 9.0.1; microsoft.netcore.app.runtime.osx-arm64 9.0.1; microsoft.netcore.app.runtime.linux-musl-arm 9.0.1; microsoft.netcore.app.runtime.win-arm 9.0.1; microsoft.netcore.app.runtime.linux-musl-arm64 9.0.1; microsoft.netcore.app.runtime.win-x64 9.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.netcore.app.runtime.win-x86: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.win-arm64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.linux-arm64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.linux-arm: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.osx-x64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.linux-x64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.osx-arm64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.win-arm: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1
- NuGet microsoft.netcore.app.runtime.win-x64: affected >= 9.0.0, < 9.0.1; fixed in 9.0.1

## 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-p54p-p3qm-8vgj (GitHub-reviewed advisory GHSA-p54p-p3qm-8vgj lists affected ranges: NuGet microsoft.netcore.app.runtime.linux-arm >=9.0.0 =9.0.0 =9.0.0 =9.0.0 =9.0.0 =9.0.0 <9.0.1; NuGet…)

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