Potential Of SSH Worm Devastation

May 10th, 2005 · No Comments

Worm

Bruce Schneier once again makes a valid point:

SSH, or secure shell, is the standard protocol for remotely accessing UNIX systems. It’s used everywhere: universities, laboratories, and corporations (particularly in data-intensive back office services). Thanks to SSH, administrators can stack hundreds of computers close together into air-conditioned rooms and administer them from the comfort of their desks.

When a user’s SSH client first establishes a connection to a remote server, it stores the name of the server and its public key in a known_hosts database. This database of names and keys allows the client to more easily identify the server in the future.

There are risks to this database, though. If an attacker compromises the user’s account, the database can be used as a hit-list of follow-on targets. And if the attacker knows the username, password, and key credentials of the user, these follow-on targets are likely to accept them as well.

A new paper from MIT explores the potential for a worm to use this infection mechanism to propagate across the Internet. Already attackers are exploiting this database after cracking passwords. The paper also warns that a worm that spreads via SSH is likely to evade detection by the bulk of techniques currently coming out of the worm detection community.

While a worm of this type has not been seen since the first Internet worm of 1988, attacks have been growing in sophistication and most of the tools required are already in use by attackers. It’s only a matter of time before someone writes a worm like this.

I only see this being a real problem if there is some kind of SSH vulnerability out there. Of course a worm could infect a lot of machines seeing as:

- people often use the same passwords for multiple accounts
- A lot of people generate keys for logging into other machines without passwords

Because of the above situations, once a worm gets into a company it can really cause havoc.