A remote code execution vulnerability exists when Microsoft Silverlight decodes strings using a malicious decoder that can return negative offsets that cause Silverlight to replace unsafe object headers with contents provided by an attacker. In a web-browsing scenario, an attacker who successfully exploited this vulnerability could obtain the same permissions as the currently logged-on user. If a user is logged on with administrative user rights, an attacker could take complete control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.