When this library is used to deserialize messagepack 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.
This is similar to a prior advisory, which provided an inadequate fix for the hash collision part of the vulnerability.
The following steps are required to mitigate this risk.
If upgrading MessagePack to a patched version is not an option for you, you may apply a manual workaround as follows:
MessagePackSecurity
.GetHashCollisionResistantEqualityComparer<T>
method to provide a collision-resistant hash function of your own and avoid calling base.GetHashCollisionResistantEqualityComparer<T>()
.MessagePackSerializerOptions
with an instance of your derived type by calling WithSecurity
on an existing options object.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.HashCode
struct (or in the pull request that merges this into the dotnet org).If you have any questions or comments about this advisory: