Microsoft Pushes Workarounds to Dodge Zero-Day Attack

While users await a patch for a flaw in the ActiveX control for the Snapshot Viewer for Microsoft Office Access, Microsoft has suggested a number of workarounds to dodge the problem.

Microsoft officials reported July 7 that they are investigating targeted attacks that take advantage of a bug in the ActiveX control for Snapshot Viewer that can be exploited via a maliciously crafted or compromised Web page. When a user views the Web page, the vulnerability could permit the attacker to execute code and gain user rights on a compromised system. The vulnerability only affects the ActiveX control for the Snapshot Viewer for the Microsoft Office Access 2000, 2002 and 2003 versions.

Among the simpler answers is to configure Internet Explorer to generate prompts before running Active Scripting or disable Active Scripting altogether in the Internet zone and the Local intranet zone. Likewise, IE can be configured to prompt before running ActiveX controls. In both cases, users can add sites they trust to a list of known good sites that will not generate the prompts.

"Many Web sites that are on the Internet or on an intranet use Active Scripting to provide additional functionality," Microsoft researchers wrote in the advisory. "For example, an online e-commerce site or banking site may use Active Scripting to provide menus, ordering forms or even account statements. You will be prompted frequently when you enable this workaround."

US-CERT also included instructions on disabling the ActiveX control for Snapshot Viewer by setting the kill bit to certain CLSIDs (class identifiers) in the Microsoft advisory.

Since successful exploitation of the attack would allow the hacker to gain the same user rights as the local user, the impact of an exploit can be limited by minimizing user rights. In addition, Internet Explorer on Windows Server 2003 and Windows Server 2008 runs in a restricted mode known as Enhanced Security Configuration that sets the security level for the Internet zone to "High" by default.

"Although these workarounds will not correct the underlying vulnerability, they help block known attack vectors," wrote Microsoft Security Response Communications Manager Bill Sisk in a blog post. "While the attack appears to be targeted, and not widespread, we are monitoring the issue and are working with our MSRA partners to help protect customers."