Microsoft Security Advisory CVE-2026-45591 – ASP.NET Core Denial of Service Vulnerability
Date: 2026-06
Affected: nuget/Microsoft.AspNetCore.SignalR.Protocols.MessagePack, nuget/Microsoft.AspNetCore.SignalR.Protocols.MessagePack, nuget/Microsoft.AspNetCore.SignalR.Protocols.MessagePack
Attack vector: dos
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-45591
CWE: CWE-400
CWE-787
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core SignalR and Blazor Server. 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 the MessagePack hub protocol used by SignalR and Blazor Server where an attacker can send deeply-nested MessagePack arrays to cause a stack overflow, resulting in a denial of service. ## Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/405 ## Affected Platforms - **Platforms:** All - **Architectures:** All ## <a name="affected-packages"></a>Affected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below ### <a name=".NET 10"></a>.NET 10 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.AspNetCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.AspNetCore.App.Runtime.linux-arm) | >= 10.0.0, <= 10.0.8 | 10.0.9 [Microsoft.AspNetCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.AspNetCore.App.Runtime.linux-arm64) | >= 10.0.0, <= 10.0.8 | 10.0.9 [Microsoft.AspNetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.AspNetCore.App.Runtime.linux-musl-arm) | >= 10.0.0, <= 10.0.8 | 10.0.9 [Mi


Mitigations:

Architectural layers (MAESTRO):