voip security* - pennsylvania state universitypdm12/cse545-s11/slides/cse545-voip.pdf · systems...

CSE545 - Advanced Network Security - Professor McDaniel Page

VoIP Security*

Professor Patrick McDanielCSE545 - Advanced Network Security

Spring 2011

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*Thanks to Prof. Angelos Keromytis for materials for these lecture slides.

Systems and Internet Infrastructure Security Laboratory (SIIS) Page

Example of toll fraud attack• Break into company PBX

‣ use them to route calls of your customers

‣ this has actually happened

http://www.theregister.co.uk/2006/06/08/voip_fraudsters_nabbed/

http://www.theregister.co.uk/2009/02/11/fugitive_voip_hacker_arrested/

“Federal authorities yesterday arrested a Miami man who they said made more than $1 million in a hacking scheme involving the resale of Internet telephone service.”

“In all, more than 15 Internet phone companies, including the one in Newark, were left having to pay as much as $300,000 each in connection fees for routing the phone traffic to other carriers without

receiving any revenue for the calls, prosecutors said.”

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Systems and Internet Infrastructure Security Laboratory (SIIS)

What is VoIP/IMS?• Protocol(s) for voice communication over IP-based

infrastructures‣ use of the Internet itself is dependent on operator

• Voice over IP: catch-all term for numerous kinds of media‣ Generally applied to voice and conference oriented products and

services, e.g., Skype

• IP Multimedia Subsystem: industry standard for IP-based multimedia communications‣ Video,

‣ Calendaring/scheduling

‣ File-sharing

‣ Collaborative editing, ...2


VoIP in the marketplace• Basis for many products/services

‣ commercial: Vonage, 3, T-Mobile/UMA, T-Mobile@Home, ...

‣ free/semi-free: Skype, GTalk, MSN, Yahoo! IM, AIM, Gizmo, ...

• Both enterprise- and consumer-oriented

‣ management simplification

‣ cost reduction

• Various architectural models

‣ centralized vs. P2P

‣ open vs. closed

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Useful Terms• codec - coder/decoder

‣ Program (not format) used to process media-specific data

• SDP - session description protocol

‣ Standard for describing media session parameters

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VoIP Protocols• Signaling‣ Responsible for call setup and

management

‣ Architectural and operational components

• Principal/endpoint naming, IP mapping, proxying, billing, access control, device configuration/management, customer support, QoS

• Data transport‣ Codecs, transport protocols

(typically RTP), QoS, content security signaling

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• Dominant mechanisms‣ Session Initiation Protocol (SIP)

‣ Unlicensed Mobile Access (UMA)

‣ Others: Skype, Asterisk, GTalk/AIM ...

‣ Useful terms‣ codec - “coder/decoder” program

(not format) used to process media-specific data

‣ SDP - session description protocol is a standard for describing media session parameters


Session Initiation Protocol (SIP)

• IETF Standardized signaling for IMS (among others)‣ Similar to HTTP‣ Text-based‣ Request/response structure‣ Stateful - highly complex state machine‣ TCP or UDP (port 5060)

• Devices‣ End-points (soft phones or hardware devices)‣ Proxy servers (local services acting on behalf of phone)‣ Registrars (local point to register with network)‣ Redirect servers (redirects calls)‣ Location server (VoIP HLR)

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SIP Flow

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SIP/RTP Call progress1. Locate endpoint* [SIP]

2. Establish call [SIP]

3. Data Transfer [RTP]

4. Hangup [SIP]

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*not shown


Call forwarding

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SIP Call Flow

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Real-time Transport Protocol (RTP)

• RTP is a pair of protocols designed to support applications with latency and jitter constraints‣ Supports the tightly controlled delivery of stream data, ‣ E.g., require some hard or soft QoS (quality of service)

• Protocols using ephemeral ports (1025-65535)‣ RTCP (Real-Time Control Protocol) provides signaling between

peers that measures and adjusts session to compensate for changing conditions

‣ RTP - the data channel that delivers the data

• SDP sometimes used to describe the session requirements, as negotiated through SIP

• Standards support a range of codecs, e.g., RFC 3016 ..,

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In reality...• Much “hidden” shared infrastructure

‣ DNS, web, NAT, TFTP, DHCP/PPPoE, Int/DiffServ, firewalls,...

• Emergent properties

‣ example: web-based UI poisoning through SIP-field manipulation

• Live aspect makes problems harder

‣ e.g., how can we filter voice spam based on content?

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SIP Security• Largely the ad hoc application of existing general-purpose

security mechanisms

‣ Authentication uses HTTP-style digest authentication

‣ TLS - when TCP is used

‣ S/MIME - used to encode/secure payloads

‣ IPsec - can be used to secure any protocols run over IP

‣ Secure Real-time Transport Protocol (SRTP) - crypto extensions to protect real-time sessions, e.g., encrypt the voice channel

• Implication: security largely pushed on infrastructure14


SIP authentication

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Unlicensed Mobile Access (UMA)

• Route GSM calls over the Internet (or a public network)‣ (usually) transparent handover between GSM and UMA

• Popular with cellphone providers‣ T-Mobile USA, Orange France, ...

• Benefits‣ reduce need to install expensive cell towers / upgrade capacity‣ reduce spectrum needs / utilization‣ improve “reception” in difficult locations ‣ depending on billing, avoid roaming charges (think

international!)

• Not to be confused with pico-/micro-/femto-cells2


UMA deployment

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Source: http://www.umatechnology.org/


UMA details• Encapsulation of GSM/3G inside IP

‣ complete frame, minus the on-the-air crypto

‣ can transfer voice, IM and (in the future) video

• Typically, devices are WiFi-supporting cellphones

‣ not strictly necessary, e.g., T-Mobile@Home in USA

• GSM frames are not natively protected

‣ A5/2 is anyway weak (i.e., broken)

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UMA Security• Handset-to-provider IPsec‣ Strong crypto and integrity protection‣ Key management (IKE, IKEv2) is a different story altogether‣ Authentication done via EAP-SIM (based on shared secret)

• The key management protocol (IKE/IKEv2) is complex‣ Perhaps “too big” to be trusted‣ More importantly, easy to misconfigure

• not as big a problem in a tightly managed environments (cellphones)

• but, UMA+smartphones spells trouble

• Provider must interface internal network with Internet‣ higher risk of compromise by external attackers‣ large numbers of potentially malicious insiders

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Threat in VoIP systems• Everyone thinks of the traditional C/I/A threats

• Loss of communication confidentiality and privacy (C)

‣ traffic analysis, content privacy

• Loss of communication integrity (I)

‣ impersonation (inbound, outgoing calls), modification of content, falsification of call records

• Loss of communication availability (A)

‣ accidental or intentional denial of service (DoS)

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Unique VoIP characteristics• Elaborate billing infrastructure in place

• Users are used to paying for telephony services

• Most charges are for relatively small amounts

• Large number of charges per billing cycle

‣ unlikely that small unauthorized charge will be noticed or challenged

• Phone infrastructure is “trusted” by average user

‣ perception carried over from PSTN

‣ not grounded on facts or experience

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VoIP-Specific Threats and Risks

• Theft of service, e.g., toll fraud, billing fraud• Social engineering, e.g., phishing/spear-phishing• Direct charge-back, e.g., immediate monetization• Risks‣ Some in common with other types of systems (software

vulnerabilities)‣ Some are very specific to IMS (protocol vulnerabilities)‣ Some are common, but are amplified by some IMS feature,

e.g., large-scale phishing through impersonation or call hijacking

• Q: are these substantially different than in cell networks?22


VoIP/IMS risk vectors• Variety of risk vectors

‣ some in common with other types of systems

• software vulnerabilities

‣ some are very specific to IMS

• protocol vulnerabilities

‣ some are common, but are amplified by some IMS feature

• large-scale phishing through impersonation or call hijacking

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VoIP Security Alliance

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6Interruption of services

5Physical access

4Service abuse

3Denial of Service

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Eavesdropping, interception, modification

ID misrepresentation

SPIT/SPAM

1Social threats

VoIPSA ThreatTaxonomy


VoIP vis. risks• Confidentiality‣ in some protocols, attackers can easily eavesdrop

• variety of available attack tools, e.g., VoMIT

• particularly a problem with SIP/RTP‣ S-RTP defined, but largely unused

‣ key management problem still unsolved (where’s my PKI?)

• Integrity‣ software vulnerabilities

• for example, as vulnerable to buffer overflows as any other piece of software

• silver lining: even simple devices are generally designed for updateability‣ mixed blessing, update mechanism can be hijacked (usually based on TFTP!)

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VoIP vis. risks• Availability

‣ susceptibility of equipment to denial of service

• general network-borne DoS attacks, powerline, ...

‣ how do you call someone to fix your problem?!

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IMS-specific problems• Architectural and protocol vulnerabilities

‣ SIP device interactions (see following slides)

• silent “snooping” via multipresence

• fraud

‣ bill bypassing

‣ hijacking of someone else’s account/PBX

‣ protocol-specific denial of service attacks

• malformed messages

• call routing games

‣ separation between signaling/data transport can be leveraged

• induce someone’s phone device to act as a DoS zombie

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Trivial protocol-specific • Single packet “phone kill”

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Privacy attack• Call someone, then report “call in progress” before ring

‣ turns phone into eavesdropping device!

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Billing avoidance and XSS

• SQL injection that targetsthe PBX’s billing records

• SQL-enabled XSS attackthat targets administrator oruser viewing call logs withbrowser!

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Reminder: call forwarding

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Protocol games: toll fraud

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draft-state-sip-relay-attack

(Attacker on hold)

Attacker

OK

ACK

Media (RTP)

INVITE Attacker

407 Authentication neededACK

407 Authentication needed

ACK

INVITE Attacker (auth)

INVITE +1 900 PREMIUM

(auth)INVITE +1 900 PREMIUM

Media (RTP)

(reverse rewrite, relayauthentication request)

(call setup)

(rewrite INVITE from Alice)

(rewrite INVITE from Alice)

PSTN call

SIP proxy/PSTN bridgeDomain D1 Alice@D1

INVITE Alice@D1

+1 900 PREMIUM


Hybrid threats• Generic threats made easy/enabled by IMS architecture‣ more realistic phishing/spear-phishing

• common attack: call by “bank officer” asking for personal information‣ remember: CallerID easy (trivial) to spoof

• (somewhat) more complicated attack: compromise SIP signaling to catch the “callback” from customer to the bank!‣ compromise of company SIP-PBX or end-device

‣ router- and routing-based attacks

‣ DNS poisoning

‣ SPIT - SPAM for voice

• Configuration problems‣ many options, many devices: easy to misconfigure

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Wrapup• The ubiquity and quality of IP-based networks is going to

lead to increasing growth of VoIP/IMS services

• However, like much of the systems themselves, security has been patched together from a loose collection of other general purpose mechanisms

‣ This is likely to lead to more opportunities for adversaries to exploit security failures and vulnerabilities

‣ Standards process like the IETF may help, but it is unclear if the market will embrace any new broad techniques

• Bottom line: this is not likely to get better soon.34

voip security* - pennsylvania state universitypdm12/cse545-s11/slides/cse545-voip.pdf · systems...

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