At the end of March, Microsoft released Security Bulletin MS02-015. This is a cumulative patch that includes new patches for two critical threats, including the CodeBase Localpath vulnerability I described two weeks ago. The bulletin refers to this vulnerability as Local Executable Invocation via ObjectTag, but it’s the same as the CodeBase Localpath vulnerability (CAN-2002-0077).

The other critical vulnerability addressed by MS02-015 is a flaw in the way Internet Explorer 5.01, 5.5, and 6.0 handle cookies. Specifically, the flaw allows some cookies to run arbitrary code on a Web site visitor’s system.

Microsoft has also released two other bulletins, MS02-016 (blocking Group Policy) and MS02-017 (unchecked buffer in multiple UNC provider), which affect Windows NT and Windows 2000 workstation and server installations as well as XP Professional.

Risk levels
MS02-015—Critical: This is a cumulative patch for IE 5.01, 5.5, and 6.0, so the threat levels for the various vulnerabilities vary, but at least two of them are rated critical by Microsoft. Taken together, the other fixes are rated critical for Internet and intranet servers, as well as client systems.

In particular, the cookie vulnerability, CAN-2002-0078, bypasses security zone restrictions allowing embedded HTML code to run with local computer zone privileges. Since this threat allows attackers to insert their own code, it is potentially much more dangerous than the CodeBase threat, which can run only executable files that are already on the system and can’t even pass any parameters to the programs.

At present, the most dangerous action known to be possible using the CodeBase attack is to simply shut down a target system.

MS02-016—Moderate: Group Policy is a Windows 2000 utility that allows administrators to specify most of the options that are available to all users on the network. This vulnerability allows an attacker to lock the Group Policy utility by opening it under “exclusive-read.” At that point, the Group Policy would no longer be applied to any new logins, either by the attacker or by anyone else, as long as it remains open.

MS02-017—Low to moderate: Exploiting this vulnerability would allow an attacker to gain higher privileges on the system.

MS02-015: This applies to IE 5.01 through 6.0. Microsoft has backtracked on its support policy limitations and included patches for IE 5.01 (for NT 4) in this update and says it will now continue to support IE 5.01 patches through June 2002. Microsoft says this change is due to “customer feedback” (i.e., complaints).

MS02-016: This applies to Windows 2000 Server, Advanced Server, and Datacenter Server.

MS02-017: This applies to XP Professional and all versions of NT 4 and Windows 2000.

Mitigating factors
MS02-015: The cookie threat has just a couple of mitigating factors. First, the user must visit a Web site or open an e-mail containing the infection and then revisit the site to trigger the planted executable. Second, local users who have restricted privileges aren’t subject to the threat. The CodeBase vulnerability has a number of mitigating factors, as detailed in my earlier article. The most important are that the attacker can run only executables that are already on the site and can’t pass any parameters to those programs.

MS02-016: The most important mitigating factor is that the administrator can determine who locked the Group Policy. Since this vulnerability can be exploited only by someone with a valid username and password, the fact that the username can be identified makes this a relatively unattractive way to attack a system. Also, this attack will only temporarily block the application of group policies. It won’t allow the attacker to alter any of the established policies permanently.

MS02-017: This can be exploited only by someone who can log on to the system interactively—and best practices recommendations say that users shouldn’t be allowed interactive logon to critical applications. On Windows 2000 systems, the attacker will also need to know the location of the buffer in memory, and this information isn’t available from Win2K.

In all instances, fixes can be applied with the supplied patches from the various Microsoft Security Bulletins, MS02-015, MS02-016, and MS02-017. The only exception is the MS02-016 vulnerability for the Windows 2000 Datacenter Server. The patch for this one is hardware-specific and must be obtained from the hardware OEM.

Final word
One of the most significant side notes in MS02-015 is the indication that customer complaints have caused Microsoft to extend support for an older application (IE 5.01). Since NT 4 is still in widespread use, especially in the government, extending support for even a few months can make a big difference to managers with tight upgrade budgets. Of additional interest is the fact that MS02-015 includes a patch for the CodeBase vulnerability, which some security specialists say Microsoft has known about for a long time but has only now addressed.