GHSA-2X83-8G95-XH59 MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps

Summary ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many distinct keys can require repeated linear scans and array copies. For large...