GHSA-f8h2-vmm9-qhj6 Microsoft Security Advisory CVE-2026-45591 – ASP.NET Core Denial of Service Vulnerability

• NuGet Microsoft.AspNetCore.App.Runtime.linux-x64: >= 8.0.0, < 8.0.28 → fixed in 8.0.28 • NuGet Microsoft.AspNetCore.App.Runtime.linux-x64: >= 9.0.0, < 9.0.17 → fixed in 9.0.17 • NuGet Microsoft.AspNetCore.App.Runtime.linux-x64: >= 10.0.0, < 10.0.9 → fixed in 10.0.9 • NuGet Microsoft.AspNetCore.App.Runtime.win-x64: >= 8.0.0, < 8.0.28 → fixed in 8.0.28 • NuGet Microsoft.AspNetCore.App.Runtime.win-x64: >= 9.0.0, < 9.0.17 → fixed in 9.0.17 • NuGet Microsoft.AspNetCore.App.Runtime.win-x64: >= 10.0.0, < 10.0.9 → fixed in 10.0.9 • NuGet Microsoft.AspNetCore.App.Runtime.osx-arm64: >= 8.0.0, < 8.0.28 → fixed in 8.0.28 • NuGet Microsoft.AspNetCore.App.Runtime.osx-arm64: >= 9.0.0, < 9.0.17 → fixed in 9.0.17 • NuGet Microsoft.AspNetCore.App.Runtime.osx-arm64: >= 10.0.0, < 10.0.9 → fixed in 10.0.9 • NuGet Microsoft.AspNetCore.SignalR.Protocols.MessagePack: >= 8.0.0, < 8.0.28 → fixed in 8.0.28 • NuGet Microsoft.AspNetCore.SignalR.Protocols.MessagePack: >= 9.0.0, < 9.0.17 → fixed in 9.0.17 • NuGet Microsoft.AspNetCore.SignalR.Protocols.MessagePack: >= 10.0.0, < 10.0.9 → fixed in 10.0.9

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 Affected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below .NET 10 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, Microsoft.AspNetCore.SignalR.Protocols.MessagePack (.NET 10) Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 10.0.0, .NET 9 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, Microsoft.AspNetCore.SignalR.Protocols.MessagePack (.NET 9) Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 9.0.0, .NET 8 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, Microsoft.AspNetC…