1. VoIP Security
Implementa3on and Protocol Problems
Sean Heelan, ISSA Seminar, May 2009

2. Overview
• VoIP background info
• Finding and exploi3ng implementa3on related
bugs
• Finding and exploi3ng protocol related bugs
• Ques3ons!
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3. Who am I
• Graduate student in Computer Science
• Primarily interested in soNware verifica3on
and program analysis
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4. VoIP Background Info
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5. Popularity of VoIP
• Why bother looking for security problems?
• ~50% of American businesses using it in some
form in 2008 (src. Computer Economics)
• Anyone here today?
• Home users – Skype, Gizmo, Blueface etc.
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6. Ambiguous graph 3me
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7. Protocols
• SIP
• SCCP
• H.225
• H.239
• H.245
• RTCP
• SDP
• MGCP
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8. Protocols
• IAX2
• Skype
• H.460
• H.450
• RTP
• STUN
• RSVP
• SS7
• ….and so on
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9. Protocols
• Why so many?
• Call setup, signalling, data transfer, route
nego3a3on, PSTN interoperability
• Each requiring a different protocol and a
different implementa3on
• Usually in C or C++
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10. Protocols
• More protocols == More ahack vectors
• Heterogeneous networks are good for an
ahacker and bad for an administrator
• Tes3ng efforts are diluted across devices and
protocols
• No public tes3ng tools available for the
majority of the protocols men3oned
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11. VoIP: A hackers dream
• Integrates the voice communica3ons of an
organisa3on into an environment the ahacker
is familiar with
• Same protocols, tools and environments
• Open standards and accessible devices
• Scary as hell when you think about it – you
just moved your en3re comms infrastructure
to our playground
• Cheers!
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12. Ahacking the implementa3on
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13. Good ol’ memory corrup3on
Servers running on Windows, Linux or other
Unix
+ Phones running on a tradi3onal OS or oNen
embedded Linux
+ Wrihen in C/C++
= Buffer overflows, NULL pointers, infinite loops
and all their friends
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14. Finding the bugs
• Fuzzing ‐ a rather effec3ve hammer for many a
nail
• Automa3cally genera3on/sending semi‐valid
requests to a target in the hope of crashing it
• Requires no understanding of the applica3on/
device internals
• Responsibly for the detec3on of a huge
percentage of security bugs
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15. Fuzzing in 2 minutes
• Genera3on based
• Muta3on based
• Extensions – Binary analysis, feedback loops,
debuggers
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16. Fuzzing example 1
INVITE sip:201@192.168.3.102 SIP/2.0
CSeq: 536870905 INVITE
Via: SIP/2.0/UDP 192.168.3.104:6060;branch=z9hG4bKmj1079uq
Content-Type: application/sdp
Content-Length: 378
s_static(“INVITE quot;)
s_string(“sip:201@192.168.3.102”)
s_static(” SIP/2.0 rnquot;)
INVITE AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA SIP/2.0
CSeq: 536870905 INVITE
Via: SIP/2.0/UDP 192.168.3.104:6060;branch=z9hG4bKmj1079uq
Content-Type: application/sdp
Content-Length: 378
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17. Fuzzing example 2
INVITE sip:201@192.168.3.102 SIP/2.0
CSeq: 536870905 INVITE
Via: SIP/2.0/UDP 192.168.3.104:6060;branch=z9hG4bKmj1079uq
Content-Type: application/sdp
Content-Length: 378
s_static(quot;Content-Length: quot;)
s_dword(378, fuzzable=True, format=“ascii”)
s_static(quot;rnquot;)
INVITE sip:201@192.168.3.102 SIP/2.0
CSeq: 536870905 INVITE
Via: SIP/2.0/UDP 192.168.3.104:6060;branch=z9hG4bKmj1079uq
Content-Type: application/sdp
Content-Length: 4294967296
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18. Building your own fuzzer
• Genera3onal fuzzing frameworks available –
Peach, Sulley, Fusil, Spike etc
• Map out the protocol in a high level
descrip3on language
• Auxiliary tools for crash detec3on and logging
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19. Feeling lazy?
• Free fuzzers for SIP – PROTOS, VoIPER
• Commercial fuzzers ‐ Codenomicon,
MuDynamics
• Use a generic fuzzer like GPF – takes a packet
capture and mutates it
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20. Does it work?
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21. And the award for epic fail goes to….
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22. Memory corrup3on summary
• Fuzzers make it simple to find bugs
• Trivial to find DoS condi3ons
• Currently no public exploits that remotely
execute malicious code on hard‐phones
• Exploi3ng vulnerabili3es in soN‐phones is
much easier, diho for servers running on
tradi3onal opera3ng systems
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23. So hard‐phones are safe then?
• Not quite …
• Run a variety of services along with the VoIP
core
• Web server, TFTP server/client, terminal
admin console
• Introduces every ahack vector available
against these services
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24. Web service ahacks
• Most hard‐phones provide a web based admin
interface, as do many servers
• Notoriously security agnos3c
• XSS, CSRF, SQL injec3on, default/no passwords,
authen3ca3on bypass
“Cisco Unified Communica7ons Manager is vulnerable to
a SQL Injec7on aBack in the parameter key of the
admin and user interface pages. A successful aBack
could allow an authen7cated aBacker to access
informa7on such as usernames and password hashes
that are stored in the database.” – Cisco 2008
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25. Web ahack example
• Snom 320 VoIP phones
• Admin interface accepts unauthorized POST
data
• Admin interface can also be used to make calls
• GNUCi3zen.org combined the above two
‘features’ for remote surveillance
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26. GNUCi3zen.org – Snom 320 ahack
• Ahacker scans for vulnerable devices by
checking for remotely accessible signature
files
• Ahacker sends POST to vic3m’s IP with data:
NUMBER=ATTACKERNUM
• Ahacker answers the incoming call
• Vulnerable device uses inbuilt receiver to
capture ambient sound and send to the
ahacker
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27. Finding web service bugs
• Simple to automate
• Standard tools for finding SQL, CSRF and XSS
bugs – w3af ahack framework
• Using SIP packets as an injec3on vector – XSS
in log data
• Far easier to find and exploit a bug in a web
interface than to create a reliable memory
corrup3on exploit
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28. Ahacking the protocols
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29. Ahacking the protocols
• Authen3ca3on
• Authoriza3on
• Encryp3on
• Same approach as every TCP/IP based service
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30. Ahacking the protocols ‐ discovery
• Many VoIP protocols are TCP based and run on
standard ports – nmap
• Specialist tools available for certain protocols
– SIPVicious, iaxscan – Can scan thousands of
hosts an hour
• Scanning random hosts turns up hoards of
easily accessible servers
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31. Ahacking the protocols ‐
authen3ca3on
• SIP and IAX2 – 2 step authen3ca3on by default
• What does that mean? – We can enumerate valid
accounts first and then crack passwords
• Account discovery search space
– Two step auth = X*X
– Single step auth = XX
Where X is the size of the username/password pool
• We’d shoot a web developer that did this but
apparently it’s OK for VoIP
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32. Ahacking the protocols ‐
authen3ca3on
• Many networks s3ll use 3 or 4 digit usernames
and passwords
• SIPVicious/iaxscan can check all possible
combina3ons in minutes
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33. Ahacking the protocols ‐ sniffing
• Not en3rely a protocol level problem
• Intercepted communica3ons can be easily
reconstructed into audio/video files –
wireshark, UCSniff
• VLAN hopping – exploi3ng networks that rely
on layer 2 protocols to allow access to the
voice LAN – Voip Hopper
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34. Taking the trunk
• Stealing individual accounts is fun and all but
how about stealing the phone company?
• Requires admin access to an accessible router
or switch
• How?
• Straight through the front door
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35. Taking the trunk
• Robert Moore – 2007, stole 10 million minutes
worth of talk 3me
• Step 1: Bought informa3on on corporate IP
addresses for $800
• Step 2: Scanned for accessible VoIP routers and
switches
• Step 3: Scanned for default passwords and
unpatched Cisco boxes
• Step 4: Profit! (Or jail in Mr. Moore’s case)
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36. Taking the trunk
• “70% of all the companies he scanned were
insecure, and 45% to 50% of VoIP providers were
insecure”
• “I'd say 85% of them were misconfigured routers.
They had the default passwords on themquot;
• “The telecoms we couldn't get into had access
lists or boxes we couldn't get into because of
strong passwords.”
‐ Source: http://www.informationweek.com
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37. Ahacking the protocols ‐ summary
• Essen3ally the same offence/defence we’ve
had for years
• Discovery, enumera3on and exploita3on
follow roughly the same paherns as most
other TCP/IP services
• Protec3ng against these problems is the same
struggle with password management, access
lists and updates
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38. Ques3on Time!
http://seanhn.wordpress.com
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