I had to evaluate the risk of a potential Terrapin attack.
- CVE-2023-48795: General Protocol Flaw
- CVE-2023-46445: Rogue Extension Negotiation Attack in AsyncSSH
- CVE-2023-46446: Rogue Session Attack in AsyncSSH
The Terrapin attack can target connections secured with ChaCha20-Poly1305 or CBC-mode ciphers with Encrypt-then-MAC. There is a theoretical vulnerability in CTR-mode ciphers combined with Encrypt-then-MAC, but it is not currently exploitable in real-world scenarios.
The attack requires an active Man-in-the-Middle.
OpenSSH and other vendors have implemented a strict key exchange countermeasure, but for it to be effective, both client and server must support it. Connecting a vulnerable client to a patched server, or vice versa, still results in a vulnerable connection.