Over the past decade, Voice over IP (VoIP) has revolutionalized the telecommunications industry. VoIP has become more prevalent than ever, and consequently more users have switched to IP-based data networks for their telephone use from the analogue Public Switched Telephone Network (PSTN).One challenge, though, is to secure and protect these VoIP connections. In this paper, we investigate a ...

VulnerabilitiesoftheReal-TimeTransport(RTP)

ProtocolforVoiceoverIP(VoIP)Traf c

MikeAdams

AcmePacketurlington,MA01803

Email:madams@acmepacket.com

MinseokKwon

DepartmentofComputerScienceRochesterInstituteofTechnology

Email:jmk@cs.rit.edu

Abstract—Overthepastdecade,VoiceoverIP(VoIP)hasrevolutionalizedthetelecommunicationsindustry.VoIPhasbe-comemoreprevalentthanever,andconsequentlymoreusershaveswitchedtoIP-baseddatanetworksfortheirtelephoneusefromtheanaloguePublicSwitchedTelephoneNetwork(PSTN).Onechallenge,though,istosecureandprotecttheseVoIPconnections.Inthispaper,weinvestigateanewapproachtodemonstratethevulnerabilityofVoIPconnections.Ourapproachmonitorsreal-timedatastreams(e.g.,RTP),andinsertspacketscontainingfraudulentvoicedataatexpectedtimesestimatedfromthemonitoring.Asfalsepacketsarewell-alignedwithoriginalpackets,wecanmaximizetheeffectsofthetestwhileminimizingthenumberofinsertedpackets.Thisminimalnumberoffalsepacketsalsohelpseschewthedetectioneffortsofdenial-of-servicedefensemechanisms.OurresultsindicatethattheinsertedpacketsatdesiredtimescanindeeddisrupttheoriginalRTPstreamwithoutanynoticeabletraf cincrease.

IndexTerms—VoiceoverIP,RTP,SIP,multimedianetworks,security,vulnerability,experiments

I.INTRODUCTION

Inrecentyears,VoiceoverIP(VoIP)technologieshavemadesigni cantprogressbothinresearchandcommer-cially[1]–[4].VoIPallowsuserstomakephonecallsoverIP-baseddatanetworksinsteadofthePublicSwitchedTele-phoneNetwork(PSTN)throughsuchtechnologiesasSIP[1],RTP[2],andH.323[5].Asthetechnologyadvances,VoIPcanprovideahigherqualityandyetmoreaffordablephoneservicethanPSTN.ThetelecommunicationindustryiswithoutadoubtmovingtowardsusingVoIPastheirmainphoneinfrastructure.

DespitetheadvancesinVoIPtechnologies,avastmajorityoftheVoIPservicesprovidedbytelecommunicationcarriersarenotsecureandvulnerabletoavarietyofmaliciousactivi-ties.Ifanattackersniffsonthenetworkbetweentwoend-usersincommunication,theattackercanseevirtuallyeverypieceofdatasentoverthewire.Theattackercaneveninsertitsownfraudulentpacketsintothewireprohibitingthevictimfromusingnetworkresources(likedenial-of-serviceattacks).

Ourgoalinthispaperistodemonstratethatadenial-of-serviceattackcanbecraftedspeci callytargetingtheVoIPnetwork,yetishardtodetectanddefeat.Whiletheattackcanbeappliedtootherreal-timedatastreams,weonlyfocusontheVoIPuseoftheG.711(U-lawandA-law)codecthatemploystheRTPprotocoltotransmitdigitizedvoicedata[2],[6].Theattackcanalsobeconsideredasthevulnerability

testofRTP.ThemainideaistoinjectfalseRTPpacketsatspeci ctimessothatthereceiveracceptsthesefalseRTPpacketswhiledroppinglegitimateones.Thistypeofattackispossiblebecausewecananticipatetheexactmomentwhenaspeci cRTPpacketisdelivered.Moreover,ISPsdonotusuallyinspectRTPpayloadsduetotheirlimitedresources,andcanseenoclearevidenceofanymaliciousbehaviorinthisattack.WealsoadoptasimilarmethodtotheshrewattackforTCPcongestioncontrol[7]tomakethisattackhardtobedetectedordefeated.Notethatthefocusisondemonstratingthatsuchanattackisfeasible,notonstudyingthereactionofVoIPclientstocallqualityunderattack.

Oursystemcomprisestwosubcomponents:1)apacketcaptureengineand2)apacketinjectionengine.ThepacketcaptureenginemonitorsthenetworkforanyRTPtraf candenablesthepacketinjectionenginewhenaVoIPcallisdetected.ThepacketinjectionenginethensynchronizeswiththeunderlyingRTPstreamandinsertsfraudulentRTPpacketsshortlyaheadofthescheduledarrivaltime.OurresultsshowthattheinsertedpacketsatdesiredtimescanindeeddisrupttheoriginalRTPstreamwithoutanynoticeabletraf cincrease.Theresultsalsoshowthatthistypeofattackcanbedoneinastealthywayandishardtotracebackviatypicaldenial-of-servicepreventionschemes.

Therestofthepaperisorganizedasfollows.InSec-tionII,wediscusstherationaleforourvulnerabilitytest,anddemonstratewhyourschemeisfeasibleinthecontextofVoIP.InSectionIII,wegiveanoverviewofrelatedwork.InSectionIV,wedescribethebasicdesignofourschemeanditsimplementationdetails.InSectionV,wepresentperformanceresultsfromourexperiments.Finally,wesummarizeourconclusionsandfutureworkinSectionVI.

II.MOTIVATION

OurvulnerabilitytestschemedoesnottechnicallydisruptRTPorforgeanyharmfulactivities.Theschemeratherdistortstheperceptionofaudioattheend-userbyaddingbogusduplicateRTPpackets.Howissuchanattackpossible?Theanswersaretwofold:1)itisnotviableforISPstoinspectRTPpayloads,and2)thereisnoclearevidenceofmaliciousbehaviorexcepttheperceptionoftheend-user.

TheISPsdonotinspectRTPpayloads,encryptandauthen-ticatemessages[8],orconductanysortofdeeppacketanalysis