Software Engineering Institute

Symantec describes Security Check as "a free web-based tool that enables users to test their computer's exposure to a wide range of on-line threats. As part of running the check, users may install an ActiveX Control, which remains on the user's system even after the check has completed." A buffer overflow has been discovered in the ActiveX control that is distributed from Symantec's web-based Security Check web site. For further technical details, please see the following documents:

• Cesar Cerrudo's advisory
• Symantec's advisory

Any user that visited Symantec's Security Check web site before June 25, 2003, when Symantec replaced the vulnerable ActiveX control, is likely to have the vulnerable control on their system. The only way to get rid of the control is to either visit Symantec's Security Check web site and run another Security Scan, or manually remove the vulnerable control. Users not following, or unaware of, either of these courses of action may be subject to an attacker installing and/or invoking a vulnerable version of the control on their system.This type of behavior could be averted by making use of Microsoft's SiteLock Template. This template "enables an ActiveX developer to restrict access so that the control is only deemed safe in a predetermined list of domains. This limits the ability of Web page authors to reuse the control for malicious purposes." Unfortunately, this Symantec ActiveX control does not make use of the SiteLock Template.

Symantec has replaced the vulnerable ActiveX control on their web site, and they recommend the following:
Recent visitors to Symantec Security Check should revisit the site and run a new Security Scan. By running a new scan, the previous ActiveX Control will be replaced by an updated ActiveX Control that fixes the buffer overflow condition. Advanced users can attempt to delete the ActiveX Control by rebooting and then going into the system folder: %SystemRoot%\Downloaded Program Files\ and delete "rufsi.dll". This must be done by using the command prompt and the user must not be on the Symantec Security Check site at the time. A removal tool has been developed and can be found here.