[Tfug] Debian SSH vulnerability

[Jeff Breadner]

Tom Rini wrote:
> On Tue, May 13, 2008 at 07:34:29PM -0700, Jeff Breadner wrote:
>   
>> John Gruenenfelder wrote:
>>     
>>> However, my understanding is also that you (and your systems) are only
>>> affected by this vulnerabilty is your keys were created *after* the package
>>> maintainer broke the random number generation and, obviously, before the
>>> bugfix was released.
>>>       
>> On my system (kubuntu 8.04), when I applied the latest updates, a new 
>> utility 'ssh-vulnkey' was installed.  You can use this to identify which 
>> keys are vulnerable to this attack vector, and which are OK.
>>     
>
> Which "might" be vulnerable.  For the past few weeks I've been seeing a
> ton of attempted logins to my home box, which was fine as no user keys
> (host key was bad 'tho) were vulnerable, so no logins.  But I figured
> something must be up...
>
> But this is the fun part.  This isn't so much a "oh, you can login to
> everyones box now with user A/pass B" but a "if you really wanna steal
> what juser has been doing here a possible vector..".  At least that's my
> take on it, but I'm not on vendor-sec anymore..
>
>   
Keys generated with the buggy code are in a predictable subset of the 
entire possible range of values, and are thus more vulnerable to a 
brute-force attack.  An attack on a 'vulnerable' key might take an 
average of 1 million login attempts to succeed instead of 1 trillion for 
a 'safe' key, for instance--I'm making those numbers up, but it 
illustrates the point.

Since I moved my public SSH port to a higher, non-standard port (>1024), 
I've had virtually no invalid login attempts on my home machine; putting 
this value in to my laptop's ~/.ssh/config file makes it completely 
transparent for me, but it's effectively invisible to all the script 
kiddies.  If you're able to change your exposed SSH port number, I'd 
really consider it.

cheers
  Jeff