LiteDB may deserialize bad JSON on object type using _type

Impact

LiteDB use a special field in JSON documents to cast diferent types from BsonDocument do POCO classes. When instance of an object are not the same of class, BsonMapper use a special field _type string info with full class name with assembly to be loaded and fit in your model. If your end-user can send to your app a plain JSON string, deserialization can load an unsafe object to fit in your model.

Patches

Version >= 5.0.13 add some basic fixes to avoid this, but is not 100% guaranteed when using Object type Next major version will contains a allow-list to select what king of Assembly can be loaded

Workarounds

• Avoid users send to your app a JSON string to be direct insert/update into database
• Avoid use classes with Object type - try use an interface when possible

If your app send a plain JSON string to be insert/update into database, prefer this:

// Bad
public class Customer {
    public int Id { get; set; }
    public string Name { get; set; }
    public Object AnyData { get; set; } // <= Avoid use `Object` base type
}

// Good
public class Customer {
    public int Id { get; set; }
    public string Name { get; set; }
    public IDictionary<string, string> AnyData { get; set; } // Will accept only key/value strings
}

References

See this workaround fix on this commit:

https://github.com/mbdavid/LiteDB/commit/4382ff4dd0dd8b8b16a4e37dfd29727c5f70f93f