On 06/11/2017 10:17 AM, Ted Roche wrote:
> For 36 hours now, one of my clients' servers has been logging ssh
> login attempts from around the world, low volume, persistent, but more
> frequent than usual. sshd is listening on a non-standard port, just to
> minimize the garbage in the logs.
>
> A couple of attempts is normal; we've seen that for years. But this is
> several each hour, and each hour an IP from a different country:
> Belgium, Korea, Switzerland, Bangladesh, France, China, Germany,
> Dallas, Greece. Usernames vary: root, mythtv, rheal, etc.
>
> There's several levels of defense in use: firewalls, intrusion
> detection, log monitoring, etc, so each script gets a few guesses and
> the IP is then rejected.
>
> In theory, the defenses should be sufficient, but I have a concern
> that I'm missing their strategy here. It's not a DDOS, they are very
> low volume. It will take them several millennia to guess enough
> dictionary attack guesses to get through, so what's the point?
Maybe they already have known-good passwords to go along with the usernames,
and they're guessing at *hosts* (or networks) where those combinations work?
Just over a decade ago, a friend who was doing sysadmin at a college
got involved in chasing down someone who had been worming his way
through college/university networks using that same general class
of strategy:
1. find usernames+passwords for staff at an arbitrary university
2. assume people with a network account at one university
probably have accounts with the same username+password
on systems at _other_ universities
(because academics collaborate across institutional boundaries)
3. grow the list hosts you can log into using #2
4. assume that some of the systems you can now log into
probably have vulnerabilities that allow you to find other
known-good username+password pairs
5. grow your list of username+password pairs using #4
5. GOTO 1
If you already have a big network of attack-bots, then there's probably
no reason to even restrict the scope to universities.
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