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December 2023. Researchers show a middlebox can truncate the SSH handshake just before NEWKEYS, downgrading your channel without triggering the hostkey warning you were trained to trust.

Type

Defensive / IR

Difficulty

Intermediate

Era

2020s

Time

8 min

Briefing

Terrapin is real but niche, attacker needs MitM. Your execs still deserve a crisp explanation.

Your role

Cryptography engineer validating `ssh -Q kex` output against the vendor bulletin before your fleet patch window.

Objective

Read the briefing, inspect sshd_config for vulnerable default KEX proposals, and grep auth logs for handshake reset lines.

Terminal environment

user: crypto
host: bastion-lab
cwd: /ssh/terrapin-workbench
steps: 3

Enter the terminalAbout 8 minutesSafe simulation

Safety note. This is a safe reconstruction. All systems, files, hosts, credentials, and outputs are simulated. Do not use these techniques on systems you do not own or have explicit permission to test.