Suppose, A is a malicious attacker. He wants to flood the mempool with fake transactions. I know if an attacker broadcasts fake transactions with no fees, then mining nodes will simply increase the transaction fees to be accepted.So, that type of transactions won't be accepted. But, suppose, if an attacker broadcasts fake transactions with high fees. Is it possible to flood the memory pools with this type of transactions?
I see the question you have, and thought I put some more info in this reply, cause comments are too short.
You seem to postulate, that it might be possible to spam the net, by sending messages with high fee, and you consider this as a possible attack vector (with "fake transaction").
To understand how the network works, it is essentially necessary to look into the validation rules of transactions, when they are sent over the network. The fees are calculated by substracting the output value from the input value. If it is above 0, then ok, else invalid.
As a particular person anyone can craft a malformed tx. The question is now, how could you do this? Again, looking at the rules, it seems impossible. When you send it, the receiving nodes and all other full nodes will verify this tx. If the tx is malformed, they will reject it, and your node will be marked as a node, which sent wrong data into the network. At a certain point in time your node will get added to the blacklist of each full node, so this malfunctioning node cannot disturb the network further.
So you would need to find a way on how to send invalid tx to other full nodes, and as Andrew and Osias replied, to the current knowledge this is impossible.