Microsoft TechNet:
"Microsoft Security Bulletin MS04-007

ASN.1 Vulnerability Could Allow Code Execution (828028)"

Impact of vulnerability: Remote Code Execution

Maximum Severity Rating: Critical

Security Update Replacement: None

Caveats: Windows NT 4.0 (Workstation, Server, and Terminal Server Edition) does not install the affected file by default. This file is installed as part of the MS03-041 Windows NT 4.0 security update and other possible non-security-related hotfixes. If the Windows NT 4.0 security update for MS03-041 is not installed, this may not be a required update. To verify if the affected file is installed, search for the file named Msasn1.dll. If this file is present, this security update is required. Windows Update, Software Update Services, and the Microsoft Security Baseline Analyzer will also correctly detect if this update is required.…

http://www.microsoft.com/technet/treeview/?url=/technet/security/bulletin/MS04-007.asp