Microsoft acknowledged the threat, which was described by representatives of Kolkata, India-based iViZ at the Defcon 16 event. Redmond offered some explanations and workarounds.
"We recognize that the claim detailed in the presentation by the researcher about BitLocker is correct," wrote Bill Sisk, security response communications manager for Microsoft, in an e-mail sent today. "This theoretical attack is only possible in targeted situations, and while probable, [it's] very unlikely."
Sisk's comments come as a retort to an announcement on Monday from iViZ, a security penetration testing company. iViZ said that it had discovered a new class of a preexisting vulnerability that allows attackers to steal computer boot passwords. The exploit bypasses the security of preboot authentication software, such as Microsoft's BitLocker hard-disk encryption tool.
The premise of iViz's argument lies in the fact that programmers who might be unaware of such bugs tend to code boot password features in a way that doesn't expunge critical information from the hard drive. It's a circumstance that could lead to "inadvertent leakage and theft," according to the company's announcement. Even the most thorough hard-drive encryption scheme may not be able to block this vulnerability.
To that end, Sisk added that the software giant has addressed such issues in Windows Vista Service Pack 1, and he encouraged "customers to update their systems accordingly."
BitLocker, first released in January 2007, is designed to guard personal and private data on mobile PCs. It comes with other protection options that can be customized to meet the needs of various end users.
"Like all full volume encryption products BitLocker has a key-in memory when the system is running in order to encrypt/decrypt data, on the fly, for the drive/s in use," wrote Sisk. "If a system is in 'Sleep mode' it is, in effect, still running."
In that vein, Microsoft encourages IT pros concerned about such bugs to consult best practices on data encryption in BitLocker, previously published by Redmond here.
Among other things, Microsoft's guidance expounds on the balance of security and usability when using BitLocker in hibernate mode.
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