Microsoft has released a new security patch to fix three known Internet Explorer vulnerabilities that have been exploited to attack Internet users.
The patch also includes a change in the basic authentication functionality in IE that Microsoft announced last week. After the patch is installed, the Web browser no longer supports the handling of user names and passwords embedded in Web URLs using the "@" symbol, Microsoft says in a statement.
The security update was released on Monday, outside of Microsoft's regular monthly patch cycle, because of the seriousness of the issues, says Mike Reavey, a Microsoft security program manager. Microsoft's official patch day this month is Tuesday, February 10.
One of the three newly patched issues is rated "critical" by Microsoft, while two are "important." By taking advantage of two of the security flaws, attackers can run or save arbitrary code on a user's PC, according to Microsoft. Another flaw allows an attacker to spoof a Web site address and potentially trick users into providing personal information.
Microsoft acknowledged the spoofing issue late last year and has been criticized for not delivering a fix sooner. Microsoft representatives say they are providing the security update as soon as possible after completing development and testing.
In Microsoft's rating system for security issues, vulnerabilities that could allow a malicious Internet worm to spread without any action required on the part of the user are rated critical. Issues that will not lead to the spread of a worm without any action taken by the user, but could still expose user data or threaten system resources, are rated important.
The problems affect all currently supported versions of Internet Explorer on all currently supported operating systems. Users are urged to install the patch immediately, Microsoft says in Security Bulletin MS04-004.
The Internet Explorer 6 Service Pack 1 version of the patch also works on Windows 98, Windows 98 Second Edition, and Windows Millennium Edition. Those versions of Windows normally would get patches only by request, because the products are in what Microsoft calls the Extended Support phase of their life cycle, Reavey says.