NOSql database systems are extremely optimized for performing retrieval and adjoining operations on large quantity of data as compared to relational models which are relatively inefficient. They are used majorly for real -time applications and statistically analyzing the growing amount of data. NoSQL databases emerging in market claim to outperform SQL databases. In Present time of technology, every person wants to save and secure its data so that no one can check their information without their permission .However, there are multifarious security issues which are yet to be resolved. In this paper, we are discussing and reviewing about the Nosql databases and their most popular security issues link (Cassandra and Mongo DB).