Oh Great, A Terrapin Broke SSH

Source: Ars Technica Oh Great, A Terrapin Broke SSH

A New Exploit For The Man In The Middle To Use

Terrapin is the name given to a new exploit, one which can break the security of SSH network traffic in certain conditions.  The first condition is that an attacker must already have successfully set up a man in the middle attack so that they can monitor traffic.  While certainly an awful thing to have happen, up until now it was believed that encrypted SSH traffic could not be modified nor usefully intercepted.  With Terrapin, it is possible to exploit weaknesses in two specific algorithms commonly used by SSH, specifically ChaCha20-Poly1305 and CBC-EtM.

The new attack is able to mess with the incremental counter that ensures what is coming over SSH was what was sent.  So far researchers have come up with two ways that could be taken advantage of.  The first is to break extensions with prevent keystroke timing attacks, as there are disturbingly accurate ways to determine what words are being typed simply by knowing the length of time between key presses.  The second is a way to force your SSH client to send and accept SHA1 traffic instead of SHA2, which is something of a nightmare nowadays.

If you head over to Ars Technica you can get technical details about Terrapin, and what we know about it so far.

The rogue extension negotiation attack targets an AsyncSSH client connecting to any SSH server sending an extension info message. The attack exploits an implementation flaw in the AsyncSSH implementation to inject an extension info message chosen by the attacker and delete the original extension info message, effectively replacing it.

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About The Author

Jeremy Hellstrom

Call it K7M.com, AMDMB.com, or PC Perspective, Jeremy has been hanging out and then working with the gang here for years. Apart from the front page you might find him on the BOINC Forums or possibly the Fraggin' Frogs if he has the time.

1 Comment

  1. JVA Terrapin esq

    of all things to corrupt it has to be the reputation of a terrapin? shame on you


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