The problem, discovered by vulnerability researcher Rajesh Sethumadhavan, is that the browser mishandles certain html tags. The flaw, he wrote in his analysis, "could be exploited by a malicious remote user to obtain sensitive local files from the victim's computer."
Sethumadhavan said the flaw exists in IE 6, and security firms such as Cupertino, Calif.-based Symantec Corp. and Redwood Shores, Calif.-based Qualys Inc. have independently confirmed it.
Specifically, the problem occurs when Internet Explorer handles the following html tags:
If these tags are preceded by the file protocol specification, a remote attacker can access arbitrary local files on a victim's system.
Late Tuesday, a Microsoft spokeswoman confirmed that the software giant is also aware of the problem.
"Microsoft has completed its investigation of new public reports of a possible vulnerability in Internet Explorer [and] has confirmed that this behavior could allow for information disclosure when a user visits a Web site," she said in an email exchange.
However, she added, "An attacker could not receive files from an affected system, but would only be able to detect the presence of files. In addition, the attacker must know the location of the file in advance."
To mitigate the risk, Symantec recommended users run all software and the Web client as a non-privileged user with minimal access rights and avoid links provided by unknown or untrusted sources. Users should also refrain from visiting sites of questionable integrity, Symantec said.