Bulletin Severity Rating:Critical - This security update resolves two privately reported vulnerabilities in Windows Media file processing. Either vulnerability could allow remote code execution if a user opened a specially crafted AVI file. If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an 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.

Read more at: Microsoft Security Bulletins