Currently when we validate BSON Binary data type, we simply skip over it without further checking if the content comply to the specification. Valid MD5s are 16-byte long but in BSON documents they can be arbitrary lengths and we do not check it. We need to make the validate command to catch this inconsistency while not for regular writes.

We can already create BSON documents with an invalid MD5 in the shell by 

> db.test.insert({u: BinData(5, "deadbeaf")})
WriteResult({ "nInserted" : 1 }) 

We should also add unit tests for this.