DTrace is not a security risk!

Recently, there was a presentation at the annual meeting of Chaos Computer Club in Berlin. As the presentation describes DTrace at some length, several have asked the question: is DTrace a security risk? The answer is an emphatic “no” – quite the contrary in fact – but it merits some explanation.

DTrace can only be used by users on the system that have the appropriate privileges (as discussed in the Security chapter of the DTrace documentation). By default, the only user with sufficient privileges to use DTrace is root – the super-user. The techniques described in the paper and in the presentation are only for use on a system that one has already compromised. Of course, once a system is compromised, all bets are off; a nefarious user can:

• Load their own daemons to act as trojan horses, potentially sniffing passwords and compromising subsequent machines

• Examine /etc/shadow and crack it to obtain cleartext for every password on the system

• Use the pre-existing Solaris observability tools (truss(1), gcore(1), mdb(1), etc.) to observe and modify arbitrary processes

• Crash and/or destroy the system beyond repair

• Load their own kernel modules to spoof arbitrary parts of the system

Yes, you can use DTrace on a compromised system to glean additional information, but everything you can do with DTrace was in principle possible before DTrace – DTrace just happens to make it a little easier. Indeed, the presentation doesn’t even discuss the ways in which a nefarious user on a compromised system can use DTrace – rather it describes how DTrace can be used to understand the system well enough to design a nefarious spoofing kernel module in the first place. And revealingly, the presentation spends quite a bit of time describing how to design a nefarious kernel module such that it evades instrumentation by DTrace.¹ The fact that time and effort were spend on DTrace evasion is telling: as a tool designed to expose the inner workings of a production system, DTrace is much more feared by the Black Hats than it is useful to them; far from being a security risk, DTrace is very much a security asset.