A replay attack (also known as a playback attack) is a form of network attack in which valid data transmission is maliciously or fraudulently repeated or delayed. This is carried out by the originator or by an adversary who intercepts the data and re-transmits it, possibly as part of a spoofing attack by IP packet substitution. This is one of the lower-tier versions of a man-in-the-middle attack . Replay attacks are usually passive in nature. Source

How it works #

• Usually needs to have access to the network in order to do this.
• Works by duplicating packets and re-sending them to a device.
• If they can replay the packets to authenticate with a server then they might be able to gain access to that server. These days passwords are hashed and then salted based on the session ID so that hashed password will only work once. Source