Microsoft Security Advisory CVE-2026-56170 – .NET Denial of Service Vulnerability

Exploitation

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

CVSS

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

EPSS

• CVE-2026-56170: 1.17% estimated exploitation activity in the next 30 days; percentile 67.57 (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-2026-56170 – .NET Denial of Service Vulnerability Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core SignalR (Microsoft.AspNetCore.App.Runtime). This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. A denial of service vulnerability exists in ASP.NET Core SignalR in .NET 8, .NET 9, and .NET 10. Stateful reconnect can be leveraged by an attacker to deny service to other users. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/TBD CVSS Details - Version: 3.1 - Severity: High - Score: 7.5 - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C - Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling) Affected Platforms - Platforms: All - Architectures: All Mitigation Factors Your ASP.NET Core app is only affected if it uses SignalR…

Published by the source

21 Jul 2026, 16:15 UTC

Last modified by the source

21 Jul 2026, 16:15 UTC

Source last checked

26 Oct 2026, 17:05 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-j8gr-8fp3-5q5h

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# Patch Next advisory brief: CVE-2026-56170

Advisory: Microsoft Security Advisory CVE-2026-56170 – .NET Denial of Service Vulnerability
IDs: CVE-2026-56170, GHSA-j8gr-8fp3-5q5h
Record: https://patchnext.com/advisories/cve-2026-56170 (revision 1, source checked 26 Oct 2026, 17:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.aspnetcore.app.runtime.linux-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.linux-musl-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.osx-x64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.linux-arm 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.win-x86 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.linux-x64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.linux-musl-arm 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.win-arm 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.linux-musl-x64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.osx-arm64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.win-x64 10.0.6, 9.0.15, 8.0.26; microsoft.aspnetcore.app.runtime.win-arm64 10.0.6, 9.0.15, 8.0.26. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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.aspnetcore.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
- NuGet microsoft.aspnetcore.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

## Suggested inspection (read-only)
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-x86: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.osx-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: 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.aspnetcore.app.runtime.linux-arm64, microsoft.aspnetcore.app.runtime.linux-musl-arm64, microsoft.aspnetcore.app.runtime.osx-x64, microsoft.aspnetcore.app.runtime.linux-arm, microsoft.aspnetcore.app.runtime.win-x86, microsoft.aspnetcore.app.runtime.linux-x64, microsoft.aspnetcore.app.runtime.linux-musl-arm, microsoft.aspnetcore.app.runtime.win-arm, microsoft.aspnetcore.app.runtime.linux-musl-x64, microsoft.aspnetcore.app.runtime.osx-arm64, microsoft.aspnetcore.app.runtime.win-x64, microsoft.aspnetcore.app.runtime.win-arm64.
- 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-j8gr-8fp3-5q5h (GitHub-reviewed advisory GHSA-j8gr-8fp3-5q5h lists affected ranges: NuGet microsoft.aspnetcore.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;…)

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