Microsoft warned on Wednesday that a flaw in its Internet Explorer browser gives attackers access to files stored on a PC under certain conditions.
"Our investigation so far has shown that if a user is using a version of Internet Explorer that is not running in Protected Mode an attacker may be able to access files with an already known filename and location," Microsoft said in a security advisory.
The vulnerability requires that an attacker knows the name of the file they want to access, it said.
The disclosure is the latest security problem to affect IE. Last month, an undisclosed vulnerability in IE 6 was used in attacks that targeted more than 20 US companies, including Google, which blamed China. The vulnerability has since been fixed by Microsoft.
The attacks led Google to announce last week that it would phase out support for Internet Explorer 6, starting with Google Apps and Google Sites in March.
The IE vulnerability disclosed on Wednesday, which is caused by incorrectly rendering local files in the browser, affects several versions, including Internet Explorer 5.01 and IE6 on Windows 2000; IE6 on Windows 2000 Service Pack 4; and IE6, IE7, and IE8 on Windows XP and Windows Server 2003, Microsoft said.
"Protected Mode prevents exploitation of this vulnerability and is running by default for versions of Internet Explorer on Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008," it said.
Microsoft hasn't seen any attacks that exploit the flaw and has yet to decide whether to repair the flaw through its monthly security patch release cycle or an urgent, out-of-cycle update.