SSH protects the world’s most sensitive networks. It just got a lot weaker | Ars Technica:

Fabian Bäumer, one of three researchers from Germany’s Ruhr University Bochum who devised Terrapin, described this approach in an email:

The Terrapin attack is a novel cryptographic attack targeting the integrity of the SSH protocol, the first-ever practical attack of its kind, and one of the very few attacks against SSH at all. The attack exploits weaknesses in the specification of SSH paired with widespread algorithms, namely ChaCha20-Poly1305 and CBC-EtM, to remove an arbitrary number of protected messages at the beginning of the secure channel, thus breaking integrity. In practice, the attack can be used to impede the negotiation of certain security-relevant protocol extensions. Moreover, Terrapin enables more advanced exploitation techniques when combined with particular implementation flaws, leading to a total loss of confidentiality and integrity in the worst case.