CVE-2026-92707

CVE-2026-92707 · MessagePack: Nested arrays can blow past buffer length limits

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 5.3 · Medium · EPSS 0.6% · Fix available

Published

2026-10-15T18:35:49.074Z

Updated

2026-10-15T20:12:15.468Z

Stack: system

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