I'm a newbie in networking, still don't quite understand about security.
Let's say a person A uses TCP to establish a TCP connection with a server. And there is a hacker B who is sniffing, so B manually creates a packet with source address and source port number to be A's and send this packet to the server, so the server thinks that this packet is from A.
I know SSL can handle this problem by including the sequence number in the MAC calculation which can be used by the server to verify the data integrity. So my questions are:
If one uses normal TCP rather than SSL, so hackers can easily create packets based on original user's info and do harm on the server, is it true?
Lets say the server is using Stateful Packet Filter type firewall, can it handle this problem? I don't think it can, because even though the firewall checks the connection table, but the created packet's source address and port number has been modified to the same as A's, so the firewall will still allow fake packet in?