---
id: "CVE-2026-70159"
kind: "vulnerability"
aliases: ["CVE-2026-70159", "GHSA-334f-vvp4-7g6p"]
title: "Microsoft Security Advisory CVE-2026-70159 - ASP.NET Core Denial of Service Vulnerability"
severity: "high"
cvss: 7.5
epss: 0.01056000031530857
exploited: false
status: "open"
category: "runtime"
products: [{"name": "Microsoft.AspNetCore.SignalR.Common", "fixed": ["10.0.13"], "affected": ">= 10.0.0, <= 10.0.12", "ecosystem": "nuget"}, {"name": "Microsoft.AspNetCore.SignalR.Common", "fixed": ["11.0.0-rc.2"], "affected": ">= 11.0.0-preview.5, <= 11.0.0-rc.1", "ecosystem": "nuget"}, {"name": "Microsoft.AspNetCore.SignalR.Common", "fixed": ["8.0.32"], "affected": ">= 8.0.0, <= 8.0.31", "ecosystem": "nuget"}, {"name": "Microsoft.AspNetCore.SignalR.Common", "fixed": ["9.0.21"], "affected": ">= 9.0.0, <= 9.0.20", "ecosystem": "nuget"}]
ecosystems: ["nuget"]
tags: ["asp.net-core", "cwe-770", "dotnet", "linux", "runtime", "self-hosted", "signalr", "windows"]
not_affected_if: ["no-signalr-stateful-reconnect", "package-version-outside-affected-ranges"]
published_at: "2026-10-13T19:19:29+00:00"
first_seen_at: "2026-10-23T19:11:32+00:00"
updated_at: "2026-10-23T23:44:52+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-334f-vvp4-7g6p", "first_seen_at": "2026-10-23T19:11:32+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-70159", "first_seen_at": "2026-10-23T23:44:52+00:00"}]
---

# Microsoft Security Advisory CVE-2026-70159 - ASP.NET Core Denial of Service Vulnerability

Microsoft.AspNetCore.SignalR.Common, part of ASP.NET Core SignalR, has a resource-exhaustion flaw in stateful reconnect: a client can block broadcasts indefinitely through MessageBuffer.ResendAsync backpressure and keep server resources allocated. An unauthenticated remote attacker can cause a denial of service on affected servers.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- nuget:Microsoft.AspNetCore.SignalR.Common affected >= 10.0.0, <= 10.0.12 fixed 10.0.13
- nuget:Microsoft.AspNetCore.SignalR.Common affected >= 11.0.0-preview.5, <= 11.0.0-rc.1 fixed 11.0.0-rc.2
- nuget:Microsoft.AspNetCore.SignalR.Common affected >= 8.0.0, <= 8.0.31 fixed 8.0.32
- nuget:Microsoft.AspNetCore.SignalR.Common affected >= 9.0.0, <= 9.0.20 fixed 9.0.21

## How to check

Run dotnet list package and look for Microsoft.AspNetCore.SignalR.Common in the affected ranges (8.0.0-8.0.31, 9.0.0-9.0.20, 10.0.0-10.0.12, 11.0.0-preview.5 to 11.0.0-rc.1).
Run dotnet --info to see the installed .NET runtime and SDK versions.
Check whether the app uses SignalR stateful reconnect.

## Fix

Update Microsoft.AspNetCore.SignalR.Common to 8.0.32, 9.0.21, 10.0.13, or 11.0.0-rc.2, matching your major line.
Install the patched .NET runtime or SDK, rebuild and redeploy self-contained apps, then restart the apps.

## Timeline

- 2026-10-23T19:11:32+00:00 ghsa https://github.com/advisories/GHSA-334f-vvp4-7g6p
- 2026-10-23T23:44:52+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-70159

## From the sources

## Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in Microsoft.AspNetCore.SignalR.Common and Microsoft.AspNetCore.SignalR.Core. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

SignalR stateful reconnect clients can indefinitely block broadcasts through `MessageBuffer.ResendAsync` backpressure and retain associated resources.

## Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/452

## 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`

- **Weakness:** CWE-770 (Allocation of Resources Without Limits or Throttling)
## Affected Platforms

- **Platforms:** Windows, Linux, macOS
- **Architectures:** All

## <a name="affected-packages"></a>Affected Packages

The vulnerability affects Microsoft .NET projects that use an affected package version listed below.

Package name | Affected version | Patched version
------------ | ---------------- | ---------------
[Microsoft.AspNetCore.SignalR.Common](https://www.nuget.org/packages/Microsoft.AspNetCore.SignalR.Common) | >= 10.0.0, <= 10.0.12 | 10.0.13
[Microsoft.AspNetCore.SignalR.Common](https://www.nuget.org/packages/Microsoft.AspNetCore.SignalR.Common) | >= 11.0.0-preview.5, <= 11.0.0-rc.1 | 11.0.0-rc.2
[Microsoft.AspNetCore.SignalR.Common](https://www.nuget.org/packages/Microsoft.AspNetCore.SignalR.Common) | >= 8.0.0, <= 8.0.31 | 8.0.32
[Microsoft.AspNetCore.SignalR.Common](https://www.nuget.org/packages/Microsoft.AspNetCore.SignalR.Common) | >= 9.0.0, <= 9.0.20 | 9.0.21

## Advisory FAQ

### <a name="how-affected"></a>How do I know if I am affected?

If using a package listed in [affected packages](#affected-packages), you're exposed to the vulnerability.

### <a name="how-fix"></a>How do I fix the issue?

1. 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.
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](https://docs.microsoft.com/dotnet/core/deploying/#self-contained-deployments-scd) 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](https://msrc.microsoft.com/report/vulnerability/new). Further information can be found in the MSRC [Report an Issue FAQ](https://www.microsoft.com/msrc/faqs-report-an-issue).

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-2026-70159](https://www.cve.org/CVERecord?id=CVE-2026-70159)

### Acknowledgements

- nono
- Vincent55 Yang (https://vincent55.tw/)

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_