CVE-2026-92707
Medium CVSS 5.3Published 2026-10-15 ยท last changed 2026-10-15
The fix
Microsoft publishes remediation for this across 4 product branches. The fixed build differs per Windows version, so the row that matters is the one matching the machine you are looking at.
| Windows version | Fixed in build | Update | Released |
|---|---|---|---|
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack on .NET 10.0 installed on Windows | 10.0.13 | configuration change | 2026-10-14 |
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack on .NET 11.0 installed on Windows | 11.0.0-rc.2 | configuration change | 2026-10-14 |
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack on .NET 8.0 installed on Windows | 8.0.32 | configuration change | 2026-10-14 |
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack on .NET 9.0 installed on Windows | 9.0.21 | configuration change | 2026-10-14 |
Having the KB is not the same as knowing whether a machine has it. Windows updates supersede each other, so the update you installed often covers a fix that shipped in an earlier one. Paste your build into the patch checker and it walks that chain for you.
What it is
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.303 and 3.1.9, deserializing attacker-controlled MessagePack data as System.Object through PrimitiveObjectFormatter can cause excessive memory allocation. The formatter allocates an object[] from each declared array length before the configured object-graph depth limit rejects the input, while nested array headers can reuse the same trailing unread bytes to satisfy per-header length validation. A comparatively small payload can therefore keep many large arrays alive at once. When an attacker can submit such data repeatedly, the allocations can cause severe managed-heap pressure, excessive garbage collection, process termination, or loss of service. Exposure requires an application to deserialize untrusted data through the affected formatter path and permit repeated attacker-controlled submissions, such as a reachable ASP.NET Core SignalR hub method with an object parameter and AddMessagePackProtocol() enabled. This issue is fixed in versions 2.5.303 and 3.1.9.
Sources
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L