Security Challenges in Hybrid Telephony Richard Hovey Communications Systems Analysis Division...

Security Challenges inHybrid Telephony

Richard HoveyCommunications Systems Analysis DivisionFebruary 8, 2007

Observations are my own and are not a reflection of views of CSAD or PSHSB.

February 8, 2007 Non-public – for Internal Use Only

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SS7

SSP

Hybrid IP-TDM Telephony

router

Broadband Phone Service

SIPDNS

IPPBX

Routing Interop (BGP)

Smartphone

Session Initiation

Protocol (SIP)

SignalingInterop

IP PBX

Security Issues

Domain Name System

Interop (DNS)

TDM NetworkIP Network

PBX


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Security Challenges in Hybrid Telephony Outline

1. Perspectives on telecom convergence• "Very-Next" Generation c.2007-2010

2. Telephony on the commodity Internet• Tutorial: basic SIP signaling• SIP Security challenges

3. Hybrid Telephony IP – TDM • Tutorial: basic SS7 signaling; SIP – SS7 Interworking• SIP-SS7 security challenges

4. 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.

Severe Risk ofSky Falling

High Risk ofSky Falling

Low Risk ofSky Falling

General Risk ofSky Falling

Significant Risk ofSky Falling

CSAD Advisory System


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TDM phone net

Broadbandcopper,cable,or fiber satellite distribution

Perspective on Convergence Very-Next Generation Residential Broadband

TDM phone net

commodity Internet

~headend

local servers

•Today: parallel access to distinct infrastructures•Future: common IP core infrastructure?

–Vision of "Carrier ISPs"–First test: adoption of “NGN Release 1”


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Tutorial: IP-IP Telephony Session Initiation Protocol Signaling (SIP)

IP Network 1 IP Network 2

SIP

LOC

IP Link [Voice Path - RTP]

IP Link [Signaling Path - SDP]

IP Link

DNSSIP

Router

Switching

Control Control


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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 sip:[email protected] SIP/2.0Via: SIP/2.0/UDP 165.135.228.98:5060Max-Forwards: 50To: Michael <sip:[email protected]>From: Kevin <sip:[email protected]>;tag=8055002911Content-type: application/sdpContent-length: 142

INVITE sip:[email protected] SIP/2.0Via: SIP/2.0/UDP 165.135.228.98:5060Max-Forwards: 50To: Michael <sip:[email protected]>From: Kevin <sip:[email protected]>;tag=8055002911Content-type: application/sdpContent-length: 142


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Tutorial: IP-IP Telephony Session Initiation Protocol Signaling (SIP)

IP Link [Voice Path]

IP Link [Signaling Path]

IP Link

❶ Kevin "calls" Michael

❷ INVITE to: sip:[email protected]

❷

❸ DNS Query

❹ INVITE❺ LS Query

❻

❻ INVITE

❼ Ringing

➑ OK

LOC

SIP SIP

DNS

Router

➒ voice (RTP)


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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 <sip:[email protected]>– 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

• Once connected phone-phone, delay acceptable– About 10% (8 msec)

• Implications for NGN?

Source: Telcordia


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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 – don’t reveal implementation– Security thru testing – use test tools to check implementation

http://www.voip-info.org/wiki/view/VOIP+Phones

http://www.voip-info.org/wiki/view/VOIP+PBX+and+Servers


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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 Source: UC Boulder

Layer Attack Vector Confidentiality

Integ-rity

Avail-ablity

App. [cont]

SIP Registration Hijacking X X X

MGCP Hijack X X X

Message modification X X

RTP Insertion

Spoof via header X X X

Cancel / bye attack X

Malformed method X

Redirect method X X

RTP SDP redirect X

RTP payload X

RTP tampering X

Encryption X X X

Default configuration X X X

Unnecessary services X X X

Buffer overflow X X X

Legacy Network X X X

DNS Availability X


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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 ΣTools

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 floodSource: UC Boulder

Layer Attack Vector Addressed by ΣTools

App. [cont]

SIP Registration Hijacking X

MGCP Hijack

Message modification

RTP Insertion

Spoof via header X

Cancel / bye attack

Malformed method X

Redirect method X

RTP SDP redirect X

RTP payload X

RTP tampering X

Encryption X

Default configuration

Unnecessary services

Buffer overflow X

Legacy Network X

DNS Availability X


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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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• 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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Voice Quality during TCP SYN attack on a network element

acceptable quality▲

◄Attack Level20% of bandwidth


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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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Columbia U – Verizon Labs



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Carrier-class Prototype• Rely on wire-speed, deep-packet inspection• 300 calls/second;10K-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 TelephonyInter-exchange Signaling (SS7)ISDN User Part (ISUP) Protocol

W X

BA

Subscriber Line

Voice Trunk

Signaling Link

❶ dial digits

❷ Initial Address Message [IAM]

❷ IAM

❸ number idle?

❹ Address Complete Message [ACM]❹ ACM

❺ ring line, transmit Caller ID

❺ ring tone❻ connect to trunk


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Tutorial: TDM-TDM TelephonyInitial Address Message (IAM)

Initial Address Message

Calling Party Number parameter

Charge Number parameter

Called Party Number parameter


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Broadband Phone Service

Tutorial: IP-TDM Telephony

router

SSP

SIPDNS MGC


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• 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. RTPT1)– 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

Tutorial: IP-TDM Telephony SIP to SS7

MGC


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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


MGC


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• INVITE message– IP-to-Wireline phone example (Kevin calls Michael from Internet)

INVITE sip:[email protected];user=phone SIP/2.0Via: SIP/2.0/UDP client.kevin.fcc.gov:5060Max-Forwards: 50To: Michael <sip:[email protected];user=phone>From: Kevin <sip:+12024180100>;tag=8055002911Content-type: application/sdpContent-length: 142



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

• Transporting SS7 over IP Network

IP

TDM

MGC

MGC STPSG

SS7IP

ISUP

M3UA

SCTP

IP

ISUP

MTP3

MTP2

MTP1

M3UA

SCTP

IP

(NIF)

MTP3

MTP2

MTP1

• 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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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

Critical Management Messages in IP and SS7 networks – just SS7 level 3


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• Only widely deployed security solution– Telcordia’s Gateway Screening Specification– Implemented at gateway STPs– Generally screens out only message headers– Doesn’t 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

http://www.sevis.com/NAM.asp


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Open Source PBXBe Your Own Phone Company

AsteriskPBX

router

SSP

TerminationProvider


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Be Your Own Phone CompanyAsterisk – Corporate PBX


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Open Source PBX Spoofing - Service & Do-It-Yourself

AsteriskPBX

router

SSP

TerminationProvider


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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 => 33,1,Answer exten => 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/agi-bin/

•Start Asterisk•Call extension 33, enter number you wish to spoof from, followed by number you wish to spoof to.

http://www.rootsecure.net/content/temp/cidspoof.agi


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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 PSTN

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 > 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?

Security Challenges in Hybrid Telephony Richard Hovey Communications Systems Analysis Division...

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