AT&T WinVNC Remote Desktop Default Configuration Vulnerability

AT&T WinVNC (Virtual Network Computing) is a freeware package available from AT&T Labs Cambridge that allows an existing desktop of a PC to be remotely available.

During WinVNC's default install process, a registry key is created that could allow a remote attacker to modify the registry entry and allow un-authenticated access to the service. The registry key - HKEY_LOCAL_MACHINE\Software\ORL\WinVNC3\ - contains the connection password, IP and query restrictions as well as other settings. By default, this key is created during install with "Administrator" and "SYSTEM" accounts having full control and the "Everybody" account having Special Access (read and modify). Please note that under Windows 2000, this key has "Standard User" privileges which can accomplish the same thing.

While it is possible for a remote attacker to exploit this using regedit (blank the password value and set the "AuthRequired" key to 0) the machine needs to be a NT 4.0 system missing the registry permission patch. If the machine is patched or is Windows 2000, you must have administrator rights or equivalent to gain access from the network. If successful, a remote attacker could gain complete access to the system.


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