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RealVNC Server does not validate client authentication method

Vulnerability Note VU#117929

Original Release Date: 2006-05-16 | Last Revised: 2008-02-26

Overview

The RealVNC Server fails to properly authenticate clients. This may allow a remote attacker to bypass authentication and gain access to the VNC server.

Description

The Virtual Network Computing (VNC) Protocol

According to RealVNC, "The VNC protocol is a simple protocol for remote access to graphical user interfaces."

RealVNC

RealVNC is an implementation of the VNC protocol.

The Problem

The RealVNC Server fails to properly authenticate clients. When a RealVNC client connects to a RealVNC server, the server provides a list of supported authentication methods. By design, the client then selects a method from the list. Due to an implementation flaw, if the client specifies that no (null) authentication should be used, the server accepts this method and authenticates the client, whether or not null authentication was offered by the server.

Note that exploit code for this vulnerability is publicly available.

Impact

A remote, unauthenticated attacker could gain access to a system running RealVNC server. If the RealVNC server runs with administrative privileges, the attacker could gain complete control of the system.

Solution

Upgrade
This issue is corrected in RealVNC version 4.1.2, RealVNC Personal Edition 4.2.3, and RealVNC Enterprise Edition 4.2.3. Refer to the RealVNC Downloads site to get a patched version.


Prompt Local Users to Accept Connections

Until updates can be applied, selecting the Prompt local user to accept connections option may prevent attackers from gaining a VNC session by exploiting this vulnerability. See the authentication section of the RealVNC user guide for more information.

Vendor Information

117929
Expand all

RealVNC

Updated:  May 16, 2006

Status

  Vulnerable

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

Refer to:

Red Hat, Inc.

Updated:  May 17, 2006

Status

  Not Vulnerable

Vendor Statement

This issue only affected version 4.1.1 of RealVNC. All Red Hat Enterprise Linux releases shipped with RealVNC versions prior to 4.1.1 and we have
verified with the exploit and by code analysis that they are not vulnerable to this issue.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

There are no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.


CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A

References

Credit

This vulnerability was reported by James Evans.

This document was written by Jeff Gennari.

Other Information

CVE IDs: None
Severity Metric: 30.49
Date Public: 2006-05-15
Date First Published: 2006-05-16
Date Last Updated: 2008-02-26 14:09 UTC
Document Revision: 47

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