A novel attack known as Terrapin was created by academic researchers. It breaks the integrity of the SSH channel when specific popular encryption modes are employed by manipulating sequence numbers during the handshake phase. By secretly truncating crucial negotiation messages, a terrapin attack weakens the security of the established connection without the client or server realizing it.
Attackers can downgrade the public key algorithms used for user authentication or disable protections against keystroke timing attacks in OpenSSH 9.5 as a result of this manipulation, which enables attackers to remove or modify messages sent across the communication channel. In addition to creating the Terrapin attack, researchers from Ruhr University Bochum also found AsyncSSH implementation vulnerabilities that might be exploited.