The First Linux Botnet

By Larry Seltzer  |  Posted 2009-03-24 Print this article Print

The main thing keeping Linux desktops out of botnets is the sophistication of their users, but the people who built Psyb0t knew most people don't pay much attention to router security.

They're calling it the first botnet designed for broadband equipment and routers, and that it is. But it's also the first of something else: Psyb0t is the first Linux botnet.

And even though it's running on hardware devices and even though it's running on Linux, and an obscure distribution of Linux at that, the basic mechanisms of it aren't that different from "conventional" botnets that run on Windows PCs. There's a lesson here.

Linux seems to be a great platform for these little embedded devices. It's small enough that it can fit in economical hardware, portable enough that you can put it on almost any processor and platform, and it's got great networking tools. This particular bot runs on Linux Mipsel devices ("Mipsel" refers to little-endian implementations on MIPS processors, generally, but not exclusively, on Linux). But it's not hard to see the same thing happening to any sufficiently large population of Internet-facing devices based on Linux or any other platform. I'm especially curious about DVRs now.

We often speak about how malware writers write for Windows because that's where the systems are and because that's where the development tools are, for malware and more generally. The same could be said now of Linux: The fact that a device runs Linux means it's easy to write binaries for it that do networking tasks, including hardening the bot and distributed denials of service.

How does Psyb0t work? The main vulnerability it seems to exploit is simply weak or nonexistent authentication. One involved device is the NetComm NB5 ADSL (asymmetric DSL) modem, earlier versions of which were administrable from the WAN side by default. In fact, some were administrable without any log-in at all. Of course updates were made, but when was the last time you applied an update to your ADSL router? I've seen vaguer reports of other vulnerabilities used.

According to DroneBL, the DNS (Domain Name System) blacklist service that found the botnet, Psyb0t appears to have been shut down just recently.

The bot will not persist if the router is power-cycled, but who does that on purpose? I also wouldn't discount the possibility that such a bot could be built to flash itself into an EPROM (erasable programmable ROM) or some other persistent memory, and then the device would probably be unsalvageable. Such an attack would be highly model-specific.

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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