Microsoft is telling systems administrators to make sure they have installed a previously announced patch to guard against security problems currently affecting websites using the company's Internet Information Services (IIS) 5.0 server.
According to an advisory released by Microsoft, companies that haven't yet installed Update 835732 detailed in Microsoft Security Bulletin MS04-011 appear to be at risk from the ongoing attack.
Users who have already deployed Windows XP Service Pack 2 RC2 appear to be protected, the company says.
The Microsoft advisory is in response to what appears to be a continuing attack against IIS 5.0 servers worldwide. The attack, first discovered last week by several security firms, involved a group of Russian hackers breaking into websites running IIS 5.0.
Stephen Toulouse, program manager at Microsoft's security response centre, says the software vendor began investigating the problem after being told about it by customers.
All early indications point to IIS 5.0 servers being affected, he says, although Microsoft hasn't yet positively identified the flaw being exploited. Evidence so far suggests that the attackers are breaking into IIS servers via a previously disclosed buffer-overrun problem in the Private Communications Transport protocol, which is part of the Microsoft Secure Sockets Layer library.
That problem was addressed with the MS04-011 patch, which is why Microsoft recommends that users install it, he says.
Meanwhile, desktop systems can be infected via two vulnerabilities in Internet Explorer, one of which has an available patch and one that doesn't, Toulouse says.
Microsoft is working on a patch for the problem, Toulouse says, without specifying when the company might have one ready. But users who keep their systems updated with the latest antivirus patches or have the high-security setting turned on while browsing the internet should be reasonably protected, he says.
Following Microsoft's advice would be a "prudent thing to do" for now, says Marty Lidner, an incident-handling team leader at the CERT Coordination Centre at Carnegie Mellon University in Pittsburgh.
He also urged them to "check to see if you have document footers enabled when they are not supposed to be."
Rather than being an attack targeted at specific sites, this appears to be an attempt by the hackers to find any vulnerable IIS server they can break into, Cooper says. "My belief is that the attackers were trying to do this very quietly maybe using bots," he says. "They didn't really care what IIS boxes were getting compromised."
Confusion remains over how widespread the infections are. According to Lidner, CERT found infections on about 100 websites of varying sizes yesterday and informed their operators of the problem. But many other websites are likely to be infected that CERT is unaware of, he says.
The number also doesn't include end-user systems that may have been compromised from visiting infected websites.
The Russian website being used to download malicious code to infected systems is also no longer available, either as a result of law-enforcement action or because the hackers have been scared away, Lidner says. That fact alone makes the threat less potent for the moment, he says.
The incident once again serves to demonstrate the need for due diligence when it comes to security, Lidner says. "This stuff happens all the time. People tend to lose sight of that," he says.
Last September, for instance, a security breach at Atlanta-based web hosting provider Interland resulted malicious code being appended to the bottom of web pages hosted on the company's servers. As with the current threat, end users that visited infected Interland-hosted sites faced the risk of malicious code being downloaded on their systems from a Russian website.