Security Challenges in Hybrid Telephony

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Security Challenges inHybrid Telephony

• Richard Hovey
• Communications Systems Analysis Division
• February 8, 2007

Observations are my own and are not a reflection
of views of CSAD or PSHSB.
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Hybrid IP-TDM Telephony
Security Issues
Session Initiation Protocol (SIP)
SignalingInterop
Domain Name System Interop (DNS)
Routing Interop (BGP)
IP PBX
TDM Network
IP Network
Smartphone
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Security Challenges in Hybrid Telephony Outline

• Perspectives on telecom convergence
• "Very-Next" Generation c.2007-2010
• Telephony on the commodity Internet
• Tutorial basic SIP signaling
• SIP Security challenges
• Hybrid Telephony IP TDM
• Tutorial basic SS7 signaling SIP SS7
  Interworking
• SIP-SS7 security challenges
• Emerging components concerns
• Open Source IP PBX
• Smartphone

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Security Challenges in Hybrid Telephony Advisory
Message

• The Sky isn't exactly falling
• but the Sea Level is rising.
• Net effect The Sky is getting closer.

CSAD Advisory System
Severe Risk of Sky Falling
High Risk of Sky Falling
Significant Risk of Sky Falling
General Risk of Sky Falling
Low Risk of Sky Falling
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Perspective on Convergence Very-Next Generation
Residential Broadband

• Today parallel access to distinct
  infrastructures
• Future common IP core infrastructure?
• Vision of "Carrier ISPs"
• First test adoption of NGN Release 1

local servers
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Tutorial IP-IP Telephony Session Initiation
Protocol Signaling (SIP)
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Tutorial IP-IP Telephony SIP Basics

• Session Initiation Protocol (SIP)
• Text-based protocol with a readable syntax,
  similar to HTTP
• Used for controlling multimedia sessions over IP
  (i.e., signaling)
• Telephony is a type of audio-only multimedia
  session
• INVITE message
• Used to establish a session analogous to ISUP
  IAM message
• IP-IP phone example (Kevin calls Michael over
  Internet)
• INVITE sipmichael_at_mkpgroup.com SIP/2.0
• Via SIP/2.0/UDP 165.135.228.985060
• Max-Forwards 50
• To Michael ltsipmichael_at_mkpgroup.comgt
• From Kevin ltsipkevin_at_fcc.govgttag8055002911
• Content-type application/sdp
• Content-length 142

INVITE sipmichael_at_mkpgroup.com SIP/2.0 Via
SIP/2.0/UDP 165.135.228.985060 Max-Forwards
50 To Michael ltsipmichael_at_mkpgroup.comgt From
Kevin ltsipkevin_at_fcc.govgttag8055002911 Content-t
ype application/sdp Content-length 142
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Tutorial IP-IP Telephony Session Initiation
Protocol Signaling (SIP)
? Kevin "calls" Michael
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IP-based Telephony SIP Signaling -Challenges

• SIP and Privacy (withholding identity)
• Identity carried in SIP URI and optional Display
  Name
• e.g., Kevin ltsipkevin_at_fcc.govgt
• Appears in numerous fields in SIP messages
• e.g., From, Contact, Reply-to
• Identity Info also appears in
• e.g., Via, Call-Info, User-Agent,
  Organization, Server
• Some are functional and have to be included
• Complicated by intermediary proxy servers that
  add headers
• and can examine the other header content

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IP-based Telephony SIP Signaling -Challenges

• Utility of protecting SIP with encryption?
• i.e., protect SIP messages with IP Security
  (IPsec) at IP Layer
• Hop-by-hop impact on Call Set-up time is
  significant
• Almost certainly unacceptable

No IPSec Proxy IPSec End-End IPSec
IP-IP 4.6 7.5 20.2
IP-TDM 7.6 9.5 21.8
TDM-IP 5.2 8.0 12.7
TDM-IP-TDM 6.9 9.3 14.3
Source Telcordia

• Once connected phone-phone, delay acceptable
• About 10 (8 msec)
• Implications for NGN?

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IP-based TelephonyVulnerabilities in SIP devices

• Dozens of vulnerabilities impacting IP-based
  telephony
• Includes commodity Internet risks at other layers
• Attacks on vulnerabilities
• can impact confidentiality, integrity,
  availability
• can trigger device hangs, crashes, restarts
• Hundreds of SIP devices software implementations
• both SIP phones and SIP Servers
• Next some approaches to mitigating risks
• Security thru obscurity dont reveal
  implementation
• Security thru testing use test tools to check
  implementation

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IP-based Telephony IP Telephony Vulnerabilities
by Protocol Layer
Layer Attack Vector Confidentiality Integ-rity Avail-ablity
Net Interface
Physical Attacks X X
ARP cache X X X
ARP flood X
MAC spoofing X X X
Internet
IP spoofing
Device X X X
Redirect Via IP spoof X X X
Malformed packets X X X
IP frag X X X
Jolt X
Transport
TCP/UDP flood X
TCP/UDP replay X X
Applicaition
TFTP server insertion X
DHCP server insertion X
DHCP starvation X
ICMP flood X
Layer Attack Vector Confidentiality Integ-rity Avail-ablity
App. cont
SIP Registration Hijacking X X X
SIP MGCP Hijack X X X
SIP Message modification X X
SIP RTP Insertion
SIP Spoof via header X X X
SIP Cancel / bye attack X
SIP Malformed method X
SIP Redirect method X X
RTP SDP redirect X
RTP RTP payload X
RTP RTP tampering X
RTP Encryption X X X
RTP Default configuration X X X
RTP Unnecessary services X X X
RTP Buffer overflow X X X
RTP Legacy Network X X X
RTP DNS Availability X
Source UC Boulder
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IP-based Telephony Security thru Obscurity?

• A vulnerable implementation becomes an explicit
  target
• e.g., Windows vulnerabilities
• SIP standard defines a "User-Agent" field
• announces software version
• can turn it off so software details are not
  revealed
• But turning off explicit identification doesn't
  really help
• sufficient info in protocol responses to
  determine software
• probing technique manipulates headers, log
  responses
• each device has a unique fingerprint
• Does suggest some security improvements
• e.g., don't respond to non-compliant messages
• e.g., randomize fields and attributes

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IP-based Telephony Security thru Obscurity?
SIP device fingerprints
Source CMU IBM Watson
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IP-based Telephony Security thru Testing

• Commercially-available VoIP testing tools
• vulnerability scanners
• Inject abnormalities into SIP messages
• E.g., one tool 4500 test cases
• but only for SIP INVITE message
• Analysis of seven testing tools
• based on lab tests of four tools claims of three
  others
• even combined, address less than half of known
  vulnerabilities

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IP-based Telephony IP Telephony Vulnerabilities
Addressed by Tools
Layer Attack Vector Addressed by STools
Net Interface
Physical Attacks
ARP cache
ARP flood
MAC spoofing
Internet
IP spoofing X
Device X
Redirect Via IP spoof X
Malformed packets
IP frag
Jolt
Transport
TCP/UDP flood X
TCP/UDP replay
Application
TFTP server insertion
DHCP server insertion
DHCP starvation
ICMP flood
Layer Attack Vector Addressed by STools
App. cont
SIP Registration Hijacking X
SIP MGCP Hijack
SIP Message modification
SIP RTP Insertion
SIP Spoof via header X
SIP Cancel / bye attack
SIP Malformed method X
SIP Redirect method X
RTP SDP redirect X
RTP RTP payload X
RTP RTP tampering X
RTP Encryption X
RTP Default configuration
RTP Unnecessary services
RTP Buffer overflow X
RTP Legacy Network X
RTP DNS Availability X
Source UC Boulder
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IP-based Telephony Denial of Service Attacks

• Background
• Brute force attacks are much easier than clever
  exploits
• Attack targets
• SIP infrastructure (SIP servers, Gateways)
• Supporting services (DNS)
• End points (SIP phones)
• Commercially available solutions for UDP/SYN
  flooding
• But currently none for SIP

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IP-based Telephony Denial of Service Attacks

• Carrier-class Analysis
• Two types of attacks used General and
  VoIP-specific
• Bi-directional Speech grade-of-service metrics
  collected
• Results
• VoIP-specific attacks effective at low rates
  against all devices
• No service let alone grade of service - to
  record
• General attacks caused a wide-range of effects
• Unexpected all devices adversely affected by TCP
  SYN attacks
• Conclusions (November 2004)
• Keep VoIP on private secured networks (off
  the public Internet) where practical
• Design DDOS mitigation products to be
  VoIP-aware

Sprint Adv. Tech. Labs
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IP-based Telephony Denial of Service Attacks
Voice Quality during TCP SYN attack on a network
element
?Attack Level 20 of bandwidth
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IP-based Telephony Denial of Service Attacks

• Current carrier-class work
• Addressing perimeter protection problem of VoIP
  service
• Strategy two detection and mitigation filters
• SIP Rule-based detection and mitigation filters
  (only valid SIP)
• Media SIP-aware dynamic pinhole filtering (only
  signaled RTP)

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IP-based Telephony Denial of Service Attacks
Columbia U Verizon Labs
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IP-based Telephony Denial of Service Attacks

• Carrier-class Prototype
• Rely on wire-speed, deep-packet inspection
• 300 calls/second10K-30K concurrent calls
• Conclusion (October 2006)
• Need to generalize methodology to cover a
  broader range of cases and apply anomaly
  detection, pattern recognition and learning
  systems

Columbia U Verizon Labs
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Tutorial TDM-TDM circuit switched
TelephonyInter-exchange Signaling (SS7)
TDM Network 1
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Tutorial TDM-TDM TelephonyInter-exchange
Signaling (SS7)ISDN User Part (ISUP) Protocol
W
X
? number idle?
? dial digits
B
A
? connect to trunk
Subscriber Line
Voice Trunk
Signaling Link
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Tutorial TDM-TDM TelephonyInitial Address
Message (IAM)
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Tutorial IP-TDM Telephony
MGC
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Tutorial IP-TDM Telephony SIP to SS7

• Media Gateway Controller (MGC)
• Also referred to as a "Softswitch" or "Call
  Agent"
• Has logical interfaces facing both networks
• Translates between SIP and ISUP messages
• SS7 protocol Level 4 (e.g. "INVITE" ? "IAM)
• Media Gateway (MG)
• Has trunking interfaces facing both networks
• Translates between IP and TDM voice streams
  (i.e. RTP?T1)
• MGC and MG can be merged in one box or kept
  separate
• Signaling Gateway (SG)
• Performs mapping of Signaling Network Messages
• SS7 protocol Level 3
• Level 3 controls congestion, balances loads,
  re-routes traffic

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Tutorial IP-TDM Telephony SIP to SS7

• Questions wrt Media Gateway Controller
• How do they map fields? e.g. "INVITE" ? "IAM?
• e.g., "From" ? "Calling Party Number and
  "Charge Number"
• What call records do they maintain?
• significant implications for Authenticating source

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Tutorial IP-TDM Telephony SIP to SS7

• INVITE message
• IP-to-Wireline phone example (Kevin calls Michael
  from Internet)
• INVITE sip12126441200_at_ss1.fcc.govuserphone
  SIP/2.0Via SIP/2.0/UDP client.kevin.fcc.gov5060
  Max-Forwards 50To Michael ltsip12126441200_at_ss
  1.fcc.govuserphonegtFrom Kevin
  ltsip12024180100gttag8055002911Content-type
  application/sdpContent-length 142

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Tutorial IP-TDM Telephony SIP to SS7
IP

• Signaling Gateway (SG) function
• Performs mapping of signaling network messages
• SS7 Level 3 congestion, balances loads, traffic
  re-routing
• Transporting SS7 over IP Network

TDM

• Bottom line SG can appear as an SS7 SP at the
  interface

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Tutorial IP-TDM Phone Service SIP-SS7 Signaling

• Questions?

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IP-TDM Phone ServiceSignaling Interworking
Vulnerabilities

• Background
• New players (CLECs) increasing the number of SS7
  access points
• Signaling Gateway looks like another SS7 SP to an
  STP
• Absence of message integrity and authentication
  in SS7
• Could use IPSec in hybrid environment but ends
  at the SG
• Recent Analysis (December 2006)
• Hijacked or misbehaving SS7 nodes
• Open to Signaling Network Management (SNM)
  injects
• Injections towards MGC can disrupt VoIP services
• Hijacked or misbehaving Signaling Gateway
• Can affect functioning of SS7 network
• Threats arising in either network due to
  misprovisioned or malicious signaling nodes are
  not confined to that network alone but may affect
  the other network as well.

GMU - UNT
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IP-TDM Phone ServiceSignaling Interworking
Vulnerabilities
Critical Management Messages in IP and SS7
networks just SS7 level 3
SS7 protocol layer and its management messages SS7 network management messages in an IP network
Message Transfer Part Level 3 MTP3 SIGTRAN layer M3UA
Signaling Network Management msgs Emergency Changeover Order Changeover Order Transfer Prohibited Transfer Controlled Transfer Restricted At Signaling Gateway, M3UA provides interworking with MTP3 function by using ASP management messages Destination Restricted Destination Unavailable Signaling Congestion Destination User Part Unavailable
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IP-TDM Phone ServiceSignaling Interworking
Vulnerabilities

• Only widely deployed security solution
• Telcordias Gateway Screening Specification
• Implemented at gateway STPs
• Generally screens out only message headers
• Doesnt check content and structure of most
  signaling messages
• Commercial products to secure SS7 are emerging
• Content-based and signal-sequence firewalls
• Network Access Meditation (Sevis)
• SS7 Security Gatekeeper (Verizon)
• Proposed MTPSec to secure SS7 network layer

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Open Source PBXBe Your Own Phone Company
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Be Your Own Phone CompanyAsterisk Corporate
PBX
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Open Source PBX Spoofing - Service
Do-It-Yourself
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Be Your Own Phone Company Spoofing - Service
Do-It-Yourself

• Things to know
• Can use standard SetCallerID(nnnnnnnnnn) command
• PBX-like not efficient for per-call spoofing
• Asterisk software is easily patched to do Caller
  ID spoofing
• Add the following lines to extension config file
  exten gt 33,1,Answer exten gt
  33,2,AGI(cidspoof.agi)
• Download the cidspoof.agi script changing line 77
  tothe correct username / hostname for VoIP
  service provider, and copy to /var/lib/asterisk/ag
  i-bin/
• Start Asterisk
• Call extension 33, enter number you wish to spoof
  from, followed by number you wish to spoof to.

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Open Source PBX

• Authentication concerns (CPN, BTN)
• manipulation now much cheaper
• isolation from traceability much greater

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Smartphone SecurityGeneral Outlook

• Virus problem seems relatively small and
  manageable
• Cell phone carriers have strong incentives to
  keep under control
• Cell phone carriers have good control points
  (e.g., gateways)
• Incidents to date haven't been widespread or fast
  spreading
• Many categorized as low-threat "proof of concept"
• Q "Is the Sky Falling?"
• A "Probably not not at the moment."
• But the ocean

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Smartphone Security General Outlook

• But cell phones are an increasingly attractive
  target
• Applications becoming more PC-like e.g., email
  attachments(smart phones make up about 5 of
  cell phones)
• Operating System uniformity increases appeal to
  hackers (i.e., Symbian, PocketPC, PalmOS
  dominate smart phones)
• Standard Markup Languages create openings (e.g.,
  java scripts)
• Phones increasingly carry sensitive info (e.g.,
  business info)
• Phones increasingly can make small financial
  charges
• by accepting "reverse SMS" micropayment charges
• i.e., there's a direct link to money
• Potential impact of viruses seems high

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Smartphone Security General Outlook

• Q What can mobile viruses do?
• Spread via Bluetooth, MMS
• Send SMS messages
• Infect files
• Enable remote control of the smartphone
• Modify or replace icons or system applications
• Install false or non-operational fonts and
  applications
• Combat antivirus programs
• Install other malicious programs
• Block memory cards
• Steal data

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Smartphone Security Symbian OS

• Dominant smartphone OS (50 of phones shipped)
• Allows user to install untrusted code
• post-installation antivirus software not as
  mature as PC
• Once installed code has access to all resources
• extract phone numbers, email
• send SMS, MMS, email make HTTP connections
• dial numbers connect via Bluetooth
• Possible to avoid detection
• run in background (server) wait for long idles
  delete logs
• user unaware of filesystem
• Possible to avoid removal, short of reflashing

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Smartphone Security Bluetooth

• Devices
• 13 of phones sold worldwide in 2004 4 in U.S.
• Distances
• Nominal range is 10 meters (often boosted to
  100m)
• Hijacking phones has been demonstrated at over a
  mile
• Suggested cipher vulnerabilities
• see Wetzel
• Observation
• a "personal networking standard" vulnerable to
  personal misjudgments and oversights

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Smartphone Security Creating the Conditions for
a Perfect Storm?
Internet
Bluetooth
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Smartphone SecurityEvolution

• By early 2005 main types of mobile viruses had
  evolved
• Very few in last 18-24 months are truly original
• Now 31 families, 170 variants.
• MMS will eventually become common method of
  propagation

Increase of known mobile malware variants
6/2004 ?
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Service ProvidersCyber Security Practice

• Background
• History
• Network Reliability Interoperability Council
  (NRIC)
• NRIC VI VII assembled Cybersecurity Best
  Practices
• applicable as appropriate voluntary,
• more of a checklist where one would like a
  culture
• Stipulation
• Technical complexity industry's superior
  expertise resources
• Regulation may not result in adoption of
  underlying philosophy

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Service ProvidersCyber Security Practice

• Question
• Are ISP businesses "Markets for Lemons" wrt
  security?
• asymmetric information gt willingness to pay only
  average price
• above average security will be driven out of the
  market?
• Challenge
• Are there approaches to improving security and
  reliability of infrastructure that benefit both
  users and providers?
• What are the incentives?
• Are ISP businesses dynamics and industry sectors
  different?