Vulnerability Note VU#197477

AT&T WinVNC allows user access to passwords and configuration via weak registry permissions

Overview

The default installation of WinVNC on certain Microsoft Windows systems permits unauthenticated access to the WinVNC service.

I. Description

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.

II. Impact

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

III. Solution

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.

Systems Affected

Vendor	Status	Date Updated
ATT	Vulnerable	25-May-2001

References

http://www.securityfocus.com/bid/1961
http://www.uk.research.att.com/vnc/winvnc.html
http://xforce.iss.net/static/5545.php

Credit

This vulnerability was discovered by Gossi The Dog <gossi@owned.lab6.com> and was reported to the Bugtraq mailing list on December 11, 2000.

This document was written by Ian A. Finlay.

Other Information

Date Public	11/19/2000
Date First Published	06/04/2001 09:08:37 AM
Date Last Updated	06/19/2001
CERT Advisory
CVE Name	CAN-2000-1164
Metric	4.70
Document Revision	67

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