Software Engineering Institute

AT&T WinVNC is a free package available from AT&T Labs Cambridge that allows an existing desktop of a PC to be available on the desktop of a remote host. This software runs on Windows 95, Windows98, Windows NT 4.0, and Windows 2000. The default installation of WinVNC creates a registry key which is used to store some of WinVNC's default settings. Some of these settings include the connection password as well as an IP based restriction list. The privileges on this registry key allow full access from the Administrator or System accounts and gives the "Everybody" group read and modify privileges. Upon creation, this key is insufficiently protected such that an attacker can modify the registry key values, which could allow unauthenticated access to the service. For example, an intruder could edit the registry and delete the value for the password field and set the key marked "AuthRequired" to 0. This would allow the intruder full access to the WinVNC service. It should be noted that on Windows 2000, network users with "Power User" privileges could edit the registry and delete the value for the password field as well. Ideally, only administrators should have access to the HKEY_LOCAL_MACHINE\Software\ORL\WinVNC3\ registry key.

This vulnerability could allow a remote attacker to modify the HKEY_LOCAL_MACHINE\Software\ORL\WinVNC3\ key and allow unauthenticated access to the service.

Use Regedit to remove the "Standard Users" & "Everybody" permissions from the HKEY_LOCAL_MACHINE\Software\ORL\WinVNC3\ registry key. Additionally, one should make sure that access to the registry is restricted to authorized personnel.