Microsoft has issued two security advisories, pointing to a "critical" flaw in its Internet Explorer Browser and a second, less severe, problem with its Windows XP operating system.
The problem with Internet Explorer stems from a security function in the software designed to stop one domain, such as a Web site, from sharing information with another domain, Microsoft said in a security bulletin.
Microsoft has discovered that such information sharing can occur when certain dialogue boxes are used.
An attacker could create a Web page that took advantage of the flaw and use it to run malicious code, possibly in the form of an executable file, on a computer used to visit the page, Microsoft said. A related vulnerability allowed an attacker to access a user's system via HTML (Hypertext Markup Language) pages that displayed help content.
The company recommended that users with Internet Explorer versions 5.01, 5.5, and 6.0 download a patch for these problems. The security bulletin, including links to the patch, is at http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS03-004.asp
The second warning - for Windows XP - concerns a problem in the Windows Redirector software that is used to access local and remote files. By sending bad data to the Redirector a hacker could cause a system fail or, if the data were crafted in a particular way, run malicious code on the user's computer, Microsoft said.
The flaw in XP couldn't be exploited remotely and an attacker would need the ability to log onto a system to run programs that use the Redirector, the company said.
Nevertheless, Microsoft said users should consider installing its security update for the problem and rated it an "important" issue.
The security bulletin, including links to the patch, is at http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS03-005.asp