The New Threats Are on the Server

Opinion: The really innovative cracking is happening on Web servers these days, and defensive research is moving in that direction too.

When I think of the prototypical botnet, I think of cable modem users with teenagers downloading programs that they assume to be other things. There are many other typical scenarios, and while theyre perfectly accurate, its probably true that most bots are hijacked broadband PCs.

But there is another type of dangerous botnet out there where you might not expect it: in Web servers and hosting farms, typically Linux boxes. The Web server software on these servers typically runs PHP, the wildly popular Web scripting language.

If you follow vulnerability tracking, youve seen the name PHP a lot over the last couple of years. The number of vulnerabilities in it has been large, and the problem is long-standing, as this story from five years ago shows. And its not entirely a matter of problems in PHP itself. There are quite a few important Web applications, especially those for inexpensive hosted Web sites, written in PHP, and these applications have their own vulnerabilities.

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Attackers know about these problems and use them to take control of the servers and use them for their own purposes—i.e. they turn them into bots. Because hosted Web servers are often managed in large farms of servers with organized naming conventions and pooled IP addresses, its not a huge step for attackers to extend their control to other systems in the farm, completely compromising it.

Ive stumbled across such sites on my own a few times over the last few years. In one typical example, I was investigating an e-Gold phishing attack I received and determined that it came from a Web server hosting a storefront site for a jewelry designer in Arizona (nice stuff, but not my wifes style). Her son ran the site and was astonished to see all these other files on the site and had no idea how they got there. It might have been some administrative oversight of his or the hosting service, but it could also have been some vulnerability in software on the el cheapo hosting service.

These servers, of course, dont typically have security software on them of any meaning, for two reasons. First its Linux, and there isnt an expectation that Linux needs such software, and second, these hosted servers are designed to run as inexpensively as possible. This is one reason theyre running PHP in the first place. This is another reason the problems go undetected or perhaps even tolerated.

Its not like the hosting service can just shut things down and screw all their customers while they straighten things out. They must either implement some workaround, potentially breaking customer applications, or upgrade software to fixed versions, also potentially breaking applications. All for a bunch of $4.95 per month hosting accounts. Sounds like a losing proposition.

So anyway, now the newly formed Web Honeynet Task Force from SecuriTeam and the ISOTF (impressive Web page) will conduct research on attacks against Web servers that install "tools, connect-back shells, bots, downloaders, malware, etc., which are all cross-platform (for Web servers) and currently exploited in the wild."

In announcing the project, big-game botnet hunter Gadi Evron said that they would not focus so much on classic code-based attacks like cross-site scripting and SQL injection, which he figures have more than enough attention, but instead on "malware and code execution attacks on Web servers and hosting farms."

Such attacks have been happening for years, but Evron says that the scale of the attacks has increased dramatically of late. In order to help admins mitigate the attacks, the project will release IP addresses and URLs for blacklisting. This is a necessary first step, but obviously not a solution.

Look for the February edition of Virus Bulletin for an article with more on the project.

Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983.

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