GreyMagic Software reported that the problem affects XMLHttpRequest, which allows Web pages in the browser to send and receive XML data via HTTP, the standard Web transfer protocol. XML is an Internet language for describing just about any sort of data.
According to the report, verified by other developers, XMLHttpRequest doesn't properly check the security settings for some types of data requests in a Web page, allowing them, if properly disguised, to request data from the user's hard drive. The Internet Explorer bug required an attacker to know the name of a file on the user's PC in order to exploit that file, but the Mozilla bug also allows the contents of directories on the local drive to be listed.
GreyMagic created a demonstration of the bug that allows a Web page to display a window for exploring the viewer's own hard drive.
The bug is found in versions of Mozilla from 0.9.7 to 0.9.9 on various operating system platforms, and in Netscape versions 6.1 and higher. The flaw doesn't affect Mozilla 1.0 release candidate 1 because XMLHttpRequest appears to be broken in that release, according to Mozilla developers.
A patch for the bug was not available as of late morning on Wednesday.
GreyMagic also criticized Netscape's system for reporting bugs, saying a 24 April attempt to report the bug was not acknowledged. Following the firm's public report of the bug, another developer reported the bug to Mozilla's bug-tracking system, whose developers have confirmed the flaw. The flaw has also been distributed on the BugTraq security mailing list.
Netscape, a division of AOL Time Warner, uses Mozilla technology in its commercial browser. Mozilla itself is open source, meaning that its original programming code is freely available for alteration and re-distribution so long as any software that uses it is made available under the same terms. Mozilla software is used in other open-source browsers, such as the Galeon browser for Linux.
Netscape was not immediately available for comment.