Entries Tagged "SSH"

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Keyboards and Covert Channels

Interesting research.

Abstract:

This paper introduces JitterBugs, a class of inline interception mechanisms that covertly transmit data by perturbing the timing of input events likely to affect externally observable network traffic. JitterBugs positioned at input devices deep within the trusted environment (e.g., hidden in cables or connectors) can leak sensitive data without compromising the host or its software. In particular, we show a practical Keyboard JitterBug that solves the data exfiltration problem for keystroke loggers by leaking captured passwords through small variations in the precise times at which keyboard events are delivered to the host. Whenever an interactive communication application (such as SSH, Telnet, instant messaging, etc) is running, a receiver monitoring the host’s network traffic can recover the leaked data, even when the session or link is encrypted. Our experiments suggest that simple Keyboard JitterBugs can be a practical technique for capturing and exfiltrating typed secrets under conventional OSes and interactive network applications, even when the receiver is many hops away on the Internet.

Posted on November 8, 2006 at 1:26 PM •

The Potential for an SSH Worm

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.

One of the countermeasures proposed in the paper is to store hashes of host names in the database, rather than the names themselves. This is similar to the way hashes of passwords are stored in password databases, so that security need not rely entirely on the secrecy of the database.

The authors of the paper have worked with the open source community, and version 4.0 of OpenSSH has the option of hashing the known-hosts database. There is also a patch for OpenSSH 3.9 that does the same thing.

The authors are also looking for more data to judge the extent of the problem. Details about the research, the patch, data collection, and whatever else thay have going on can be found here.

Posted on May 10, 2005 at 9:06 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.