Subject: [Sshmgmt] Impact of missing SSH hostkey verification in the light of pubkey authentication

From: [email-masked]
Date: Thu, 13 Mar 2014 12:34:03 -0700

Hi,

since I read gremwell's blogpost [1] a few years ago I believed to be safe
against MITM attacks even without properly performing hostkey checks as
long as I use pubkey authentication, but in section 2.2.6 ("Dangers of
Unverified and Shared Host Keys") of the last draft version [2] it says:

"
   Many file transfer applications, privileged access management
   systems, and systems management applications do not check host keys
   for hosts that they connect to.  This permits a man-in-the-middle
   attack to be performed in the network.  Many tools are available for
   this and any device connected to a network through which the
   connection goes can be used for the attack - including, e.g.,
   reprogrammed smart switches.

   *Man-in-the-middle attacks are a risk regardless of the authentication
   method* if hosts keys are not properly verified.  The attack permits
   injection of arbitrary commands into the session, and reading and
   modifying any transferred files (including injection of bogus file
   transfers).  A successful man-in-the-middle attack from the network
   gives the same power as being able to use a trust relation leading to
   the destination host.
"

So that means that even ssh connections established via pubkey auth are
vulnerable to MITM attacks if the client doesn't properly perform hostkey
checking?
Do you know of a tool that implements MITM attacks against pubkey
authentication?

thanks for clarifying!
Simon

[1] http://www.gremwell.com/ssh-mitm-public-key-authentication
[2] http://tools.ietf.org/id/draft-ylonen-sshkeybcp-01.txt