Use of Weak Hash in MessagePack

Summary

The MessagePack is an extremely fast serializer for C#. When this library is used to deserialize messagepack versions through 2.5.172 and 2.6.95-alpha through 3.0.208-rc.1 data from an untrusted source, there is a risk of a Denial of Service attack by an attacker that sends data contrived to produce hash collisions, leading to large CPU consumption disproportionate to the size of the data being deserialized. A manual workaround is as follows: 1. Declare a class that derives from "MessagePack Security.". 2. Override the "GetHashCollisionResistantEqualityComparer<T>" method to provide a collision-resistant hash function of your own and avoid calling "base. GetHashCollisionResistantEqualityComparer<T>()". 3. Configure a "MessagePackSerializerOptions" with an instance of your derived type by calling "WithSecurity" on an existing options object. 4. Use your custom options object for all deserialization operations. This may be by setting the "MessagePackSerializer.DefaultOptions" static property if you call methods that rely on this default property, and/or by passing in the options object explicitly to any "Deserialize" method.