News

Microsoft Releases Patches for IE, Windows

• By Scott Bekker
• November 30, 1999

A vulnerability in an optional component of Internet Explorer 5 could allow a malicious user to gain additional privileges on a Windows NT machine that allowed the user to create or change files. Internet Explorer 5 includes an Offline Browsing Pack that is not installed by default. The Offline Browsing Pack provides a Task Scheduler that replaces the native Windows NT Schedule Service (also known as the AT Service). A vulnerability in the Task Scheduler poses a privilege elevation risk and could allow normal users to execute code on the local machine in the system context. The Windows NT Schedule Service does not have this flaw.

The IE 5 Task Scheduler controls who can create and submit "AT jobs." The utility that is used to create AT jobs can only be run by an administrator, and the Task Scheduler will only execute AT jobs that are owned by administrators. However, if a malicious user had change access to an existing file owned by an administrator, the malicious user could modify it to be a valid AT job and place it in the appropriate folder for execution. This would bypass the control mechanism and allow the job to be executed.

This vulnerability would primarily affect machines that allow normal users to interactively log onto them. The patch eliminates the vulnerability by digitally signing all AT jobs at creation time, and verifying the signature at execution time. Only Internet Explorer 5, when run on a Windows NT 4.0 system, is affected by this vulnerability. The vulnerability is eliminated by Internet Explorer 5.01, available at: http://www.microsoft.com/msdownload/iebuild/ie501_win32/en/ie501_win32.htm.

Microsoft has also announced a vulnerability in Windows 95 and 98 caused by a legacy mechanism for caching network security credentials. The vulnerability could allow a user's plain text network password to be retrieved from the cache.

Windows for Workgroups provided a RAM-based caching mechanism that cached the user's plain text network credentials for use by real-mode command-line networking utilities. Part of this mechanism was carried forward into Windows 95 and 98, even though it is not used by either operating system. A malicious user could query this mechanism to obtain the network credentials of the last person to use the machine for network access, as long as they had physical access to the machine and it had not been rebooted since the last networking session.

Windows 95 and 98 are affected by this vulnerability. The patch for Windows 95 is available at: http://download.microsoft.com/download/win95/update/ 168115/w95/en-us/168115us5.exe. The patch for Windows 98 is available at: http://download.microsoft.com/download/win98/update/ 168115/w98/en-us/168115us8.exe.