The Terrapin attack is a cryptographic attack on the commonly used SSH protocol that is used for secure command-and-control throughout the Internet. The Terrapin attack can reduce the security of SSH by using a downgrade attack via man-in-the-middle interception.[1][2][3] The attack works by prefix truncation; the injection and deletion of messages during feature negotiation, manipulating sequence numbers in a way that causes other messages to be ignored without an error being detected by either client or server.[4]

According to the attack's discoverers, the majority of SSH implementations were vulnerable at the time of the discovery of the attack (2023).[4] As of January 3rd, 2024, an estimated 11 million publicly accessible SSH servers are still vulnerable.[5] However, the risk is mitigated by the requirement to intercept a genuine SSH session, and that the attack can only delete messages at the start of a negotiation, fortuitously resulting mostly in failed connections.[4][6] Additionally the attack requires the use of either ChaCha20-Poly1305 or a CBC cipher in combination with Encrypt-then-MAC modes of encryption.[7] The SSH developers have stated that the major impact of the attack is the capability to degrade the keystroke timing obfuscation features of SSH.[6]

The designers of SSH have implemented a fix for the Terrapin attack, but the fix is only fully effective when both client and server implementations have been upgraded to support it.[1] The researchers who discovered the attack have also created a vulnerability scanner to determine whether an SSH server or client is vulnerable.[8]

The attack has been given the CVE ID CVE-2023-48795[9].[3] In addition to the main attack, two other vulnerabilities were found in AsyncSSH, and assigned the CVE IDs CVE-2023-46445 and CVE-2023-46446.[3]

References

  1. 1 2 Goodin, Dan (2023-12-19). "SSH protects the world's most sensitive networks. It just got a lot weaker". Ars Technica. Retrieved 2023-12-20.
  2. ↑ Bäumer, Fabian; Brinkmann, Marcus; Schwenk, Jörg (2023-12-19), Terrapin Attack: Breaking SSH Channel Integrity By Sequence Number Manipulation, retrieved 2023-12-20
  3. 1 2 3 "Terrapin attacks can downgrade security of OpenSSH connections". BleepingComputer. Retrieved 2023-12-20.
  4. 1 2 3 Jones, Connor. "SSH shaken, not stirred by Terrapin downgrade vulnerability". www.theregister.com. Retrieved 2023-12-20.
  5. ↑ "Nearly 11 million SSH servers vulnerable to new Terrapin attacks". BleepingComputer. Retrieved 2024-01-07.
  6. 1 2 "OpenSSH 9.6 release notes". openssh.com. 2023-12-18.
  7. ↑ "Terrapin Attack". terrapin-attack.com. Retrieved 2024-01-07.
  8. ↑ "Release v1.1.0 · RUB-NDS/Terrapin-Scanner". GitHub. Retrieved 2024-01-07.
  9. ↑ "CVE-2023-48795". cve.org. Retrieved 2024-01-16.


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