CVE-2026-45591: Microsoft ASP.NET Core uncontrolled resource consumption

CVE-2026-45591 · Severity: high · CVSS 7.5 · Published 2026-06-09

A security vulnerability has been identified in Microsoft ASP.NET Core components used for real-time web communication (SignalR and Blazor Server). An attacker can exploit this flaw to crash the web application, leading to a service outage. This affects businesses using these frameworks to provide interactive, real-time features to their users.

Technologies: Microsoft Asp.Net Core, Microsoft.AspNetCore.App.Runtime.linux-x64 (NuGet), Microsoft.AspNetCore.App.Runtime.osx-arm64 (NuGet), Microsoft.AspNetCore.App.Runtime.win-x64 (NuGet), Microsoft.AspNetCore.SignalR.Protocols.MessagePack (NuGet). Vendors: Microsoft, NuGet.

Quick answers

Is CVE-2026-45591 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-45591 being exploited in the wild.
How severe is CVE-2026-45591?
High severity, with a CVSS score of 7.5, published 9 June 2026.
Which products and versions are affected?
Microsoft Asp.Net Core 8.0.0 - 8.0.27, 9.0.0 - 9.0.16, 10.0.0 - 10.0.8; Microsoft.AspNetCore.App.Runtime.linux-x64 (NuGet) ECOSYSTEM:introduced=8.0.0,fixed=8.0.28; Microsoft.AspNetCore.App.Runtime.osx-arm64 (NuGet) ECOSYSTEM:introduced=8.0.0,fixed=8.0.28; Microsoft.AspNetCore.App.Runtime.win-x64 (NuGet) ECOSYSTEM:introduced=8.0.0,fixed=8.0.28; and 1 more.
Is there a fix for CVE-2026-45591?
Yes. Microsoft.AspNetCore.App.Runtime.linux-x64 (NuGet): upgrade to 8.0.28 or later; Microsoft.AspNetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 8.0.28 or later; Microsoft.AspNetCore.App.Runtime.win-x64 (NuGet): upgrade to 8.0.28 or later; Microsoft.AspNetCore.SignalR.Protocols.MessagePack (NuGet): upgrade to 8.0.28 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-45591 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-45591?
Check whether you run Microsoft Asp.Net Core, Microsoft.AspNetCore.App.Runtime.linux-x64 (NuGet), Microsoft.AspNetCore.App.Runtime.osx-arm64 (NuGet) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • Microsoft.AspNetCore.App.Runtime.linux-x64 (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.AspNetCore.App.Runtime.linux-x64 --version 8.0.28
  • Microsoft.AspNetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.AspNetCore.App.Runtime.osx-arm64 --version 8.0.28
  • Microsoft.AspNetCore.App.Runtime.win-x64 (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.AspNetCore.App.Runtime.win-x64 --version 8.0.28
  • Microsoft.AspNetCore.SignalR.Protocols.MessagePack (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.AspNetCore.SignalR.Protocols.MessagePack --version 8.0.28

Technical details

A denial of service vulnerability (CWE-400) exists in the MessagePack hub protocol implementation within ASP.NET Core SignalR and Blazor Server. The root cause is insufficient validation of nested structures, allowing a remote, unauthenticated attacker to send specially crafted, deeply-nested MessagePack arrays. This triggers a stack overflow during deserialization, resulting in an immediate crash of the application process. The vulnerability affects .NET 8, 9, and 10 environments. Patches are available in versions 8.0.28, 9.0.17, and 10.0.9.

Affected products

  • Microsoft ASP.NET Core 8.0.0 - 8.0.27, 9.0.0 - 9.0.16, 10.0.0 - 10.0.8
  • Microsoft Microsoft.AspNetCore.SignalR.Protocols.MessagePack 8.0.0 - 8.0.27, 9.0.0 - 9.0.16, 10.0.0 - 10.0.8

Identifiers

  • CVE-2026-45591
  • GHSA-f8h2-vmm9-qhj6

Timeline

  • 2026-06-09: disclosed
  • 2026-06-09: advisory
  • 2026-06-15: patched: Advisory updated with final patch details

References

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