Fabric is an implementation of blockchain. Blockchain guarantees safety because it is decentralized. Any activity on the network will be noticed by all the other nodes. And a block in a block chain contains information/data regarding the previous node and that previous node contains data about its previous node and so on. So, for a user to change the data in the block, he has to modify all the block right from the beginning of the chain. And to approve this, the malicious node has to have a majority of at least 51% of the network. All this makes it difficult for malicious activity.
And to answer your question, you can use to following approach to handle malicious node in the network.
1. You can control throughput and a potential maximum per port or user per second.
2. Create a transaction fee which would limit the limit the malicious activity.
3. Once you detect which node is malicious, remove that node from the network.