A flaw in Vista's networking has been found that can crash the system, but no fix is expected until the next service pack

A flaw has been found in Windows Vista that could allow rootkits to be hidden or denial-of-service attacks to be executed on computers using the operating system.

The vulnerability was found by Thomas Unterleitner of Austrian security company Phion and was announced Friday. Unterleitner told ZDNet UK on Friday that Phion told Microsoft about the flaw in October but that he understood a fix would only be issued in the next Vista service pack.

According to Unterleitner's disclosure of the flaw, the issue lies in the network input/output subsystem of Vista. Certain requests sent to the iphlpapi.dll API can cause a buffer overflow that corrupts the Vista kernel memory, resulting in a blue-screen-of-death crash.

"This buffer overflow could (also) be exploited to inject code, hence compromising client security," Unterleitner said.

Unterleitner told ZDNet UK via e-mail that the "exploit can be used to turn off the computer using a (denial-of-service) attack." He also suggested that, because the exploit occurs in the Netio.sys component of Vista, it may make it possible to hide rootkits.

Using a sample program, Unterleitner and his colleagues ascertained that Vista Enterprise and Vista Ultimate were definitely affected by the flaw, with other versions of Microsoft's operating system "very likely" to be affected as well. Both 32-bit and 64-bit versions are vulnerable. Windows XP is not affected.

Asked about the severity of the flaw, Unterleitner pointed out that administrative rights were needed to execute a program calling the function that would cause the buffer overflow. However, he also said it was possible--but not yet confirmed--that someone could use a malformed DCHP packet to "take advantage of the exploit without administrative rights."

"We have worked together with Microsoft Security Response Center in Redmond since October 2008 to locate, classify and fix this bug," Unterleitner wrote. "Microsoft will ship a fix for this exploit with the next Vista service pack."

Microsoft told ZDNet UK on Friday that it had investigated the issue, but was "currently unaware of any attacks trying to use the vulnerability or of customer impact." It could not, however, confirm the inclusion of a fix for the problem in the next as-yet-unreleased service pack for Vista, nor give the release date for that service pack.