Vulnerability Note VU#598581

AT&T WinVNC server contains buffer overflow in Log.cpp

Overview

A buffer overflow in the WinVNC server on Windows systems can allow an intruder to gain control of the VNC server and execute arbitrary code with the privileges of the user running the server.

I. Description

AT&T WinVNC is a free software package available from AT&T Labs Cambridge that allows users to interact with the desktop of a remote Windows host. By providing a specially crafted HTTP request to the VNC server, an attacker can overflow a buffer in Log.cpp, resulting in access to the VNC server and the ability to execute arbitrary code with the privileges of the user running the server. It is worth noting that the VNC server does not listen on 80/tcp by default. See the following url:

http://www.uk.research.att.com/vnc/faq.html#q52

II. Impact

Local and remote users can execute arbitrary code with the privileges of the user running the server.

III. Solution

Apply this patch while inside the vnc_winsrc/winvnc
directory:

--- Log.cpp Mon Jan 15 18:17:46 2001
+++ Log.cpp Mon Jan 15 18:18:31 2001
@@ -130,7 +130,7 @@

// - Write the log message
TCHAR line[LINE_BUFFER_SIZE];
- vsprintf(line, format, ap);
+ _vsnprintf(line, sizeof(line)-sizeof(TCHAR), format, ap);
ReallyPrintLine(line);
}

Systems Affected

Vendor	Status	Date Updated
ATT	Vulnerable	15-Jun-2001

References

http://www.securityfocus.com/bid/2306
http://www.uk.research.att.com/vnc/

Credit

Our thanks to CORE SDI for the information contained in their bulletin.

This document was written by Ian A. Finlay and is based on information obtained from a Core SDI Security Advisory.

Other Information

Date Public	01/29/2001
Date First Published	06/28/2001 11:57:38 AM
Date Last Updated	06/28/2001
CERT Advisory
CVE Name	CAN-2001-0168
Metric	12.60
Document Revision	32

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