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Attacks exploit Windows DNS server flaw

Only workarounds for now

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Attackers are targeting a flaw in the DNS service for Windows server OSes that could hijack the computers that run them, Microsoft warns. The software behemoth advises admins to employ workarounds pending completion of its investigation.

The vulnerability affects Windows 2000 Server, Service Pack 4 and SP 1 and SP2 versions of Windows Server 2003, according to this Microsoft advisory. DNS functionality exposed over port 53 is not at risk. Nor are Windows 2000 Professional, Windows XP and Windows Vista.

An attack can be carried out by executing a stack-based buffer overrun in the DNS Server's remote procedure call (RPC) interface. A successful exploit, in which a specially crafted RPC packet is sent to a targeted machine, could allow an attacker to run code in the security context of the DNS, which by default runs full privileges.

Without elaborating, Microsoft said it is aware of "limited attacks" using the DNS flaw. Fortunately, the SANS Internet Storm Center was a bit more forthcoming, saying it has learned of two US universities that have been attacked, in each case in early April from a source located at 61.63.227.125.

According to SANS, the attack commences with a TCP scan of ports 1024-2048, followed by a TCP connection to the port running the vulnerable RPC service. A Shellcode binds to TCP port 1100 and a VBscript is uploaded, which downloads an executable DUP.EXE. Voila: the machine is pwnd.

It's been a busy few weeks for Microsoft's security peeps. Last week, the company rushed out an emergency update to patch a critical hole in the way Windows handles customized cursors. On Tuesday, the company released a host of fixes as part of its monthly patch cycle. But even before savvy users had a chance to install them, miscreants were already tinkering with several new exploits targeting Microsoft products.

Microsoft has yet to announce plans for a patch. In the meantime, it is providing instructions for workarounds, which include disabling remote access of DNS using RPC. Those who want to automate the disabling of RPC from a large number of domain controllers can find help here. ®

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