Microsoft Warns of New DNS Attacks

Microsoft Corp.'s far from silent spring continues.

Yesterday, the software giant published a new security advisory warning of a new spate of attacks targeting a DNS vulnerability in its Windows server operating systems.

Microsoft says the "limited attack" targets a DNS vulnerability which affects Windows 2000 Server (SP4) and Windows Server 2003 (all versions). Windows client operating systems aren't affected, Redmond said, because they don't ship with Microsoft's DNS service.

The new DNS attacks, like other recent exploits, could allow a remote code execution scenario, assuming that an attacker successfully compromises a vulnerable system. In this case, Microsoft confirms, the attacker could run code in the all-powerful Local System context -- the same security context in which the Windows DNS service itself runs.

The attack targets the Windows DNS RPC interface, which appears to be susceptible to a classic stack-based buffer overrun exploit. One workaround, Microsoft indicated, is to disable support for DNS remote management over RPC in the Windows registry. This doesn't actually patch the underlying vulnerability, the software giant conceded, but does effectively insulate DNS from attack. This is also a recommended security practice, experts said -- although it isn't always feasible, given DNS topologies in many organizations.

"It depends on whether you need to be able to remotely manage the organization in various physical proximities, so there's good reason for [DNS servers] to be in disparate locations, and therefore a logical reason why you might need to do [DNS management over RPC]," said Russ Cooper, a senior information security analyst with Cybertrust Inc., and founder/editor of the NTBugtraq mailing list. "That said, why not use Terminal Services instead? Then you can disable the RPC and use [RDP], assuming you've enabled Terminal Services [on remote DNS servers]."

Microsoft hasn't yet issued a patch; in its security advisory, Redmond said it is investigating the attacks and could issue a patch in the future.

The new warning comes only days after security researchers disclosed the possibility of several new vulnerabilities in Microsoft's Word 2007 application, as well as a vulnerability in its Windows .HLP file implementation. Redmond earlier this week published four critical security bulletins which collectively patch six vulnerabilities in its Windows and Windows Content Management Server (CMS) offerings, as well.

Cooper, for his part, doesn't necessarily think there's been an uptick in attack activity. He conceded, however, that targeted attacks seem to be a more frequent occurrence.

"To be honest, I haven't thought of it in that way [as an uptick in general attack activity]," Cooper said. "I guess if you group [the new DNS attack] together with the alleged zero days in Microsoft Office, then, yes, you could say there's an increase in targeted attack activity. We have been concerned with targeted attacks for about a year now, but in general is there more attack traffic? I would say no. It's still the same old attack traffic coming across as attachments in e-mail -- just a lot more [targeted activity]."

About the Author

Stephen Swoyer is a contributing editor for Enterprise Systems. He can be reached at [email protected].