Mitigating Attacks on Open Functionality in SMS-Capable Cellular Networks Patrick Traynor, William Enck, Patrick McDaniel, and Thomas La Porta | MobiCom ‘06 CS712 병렬처리특강 | Dependable Software Lab. | Lee Dong Kun

KAIST | Dependable Software Lab | Direito Contents  Introduction  Related Work  System/Attack Characterization  Mitigation Technique  Current Solution  Queue Management  Resource Provisioning  Simulation Result  Conclusion 2 KAIST | Dependable Software Lab | Direito

Introduction  Cellular Network System  Traditional cellular(phone) network system provided closed voice comm.  Currently cellular network system provides opened voice and data comm.  Service Interconnection  Phone network service and Internet service are interconnected by telecommunication provider.  Problems  Traditional phone networks had designed for only homogeneous closed system.  But current phone networks tightly interconnected with phone network and Internet.  Unexpected security problems occur  Heavy SMS traffics can flood over the phone network through Internet services. 3 KAIST | Dependable Software Lab | Direito

Contents  Introduction  Related Work  System/Attack Characterization  Mitigation Technique  Current Solution  Queue Management  Resource Provisioning  Result and Discussion  Conclusion 4 KAIST | Dependable Software Lab | Direito

Related Work | Vulnerability and Approaches  Traditional Solution  Disconnection method  Disconnect from external network – effective way in the past  Not effective anymore, because of new access pattern and service  Vulnerability  Telecomm. Networks are not only systems to suffer from vulnerabilities related to expanded connectivity.  Systems less directly connected to the Internet have also been subject to attack.  DoS(Denial of Service) Attack  Traditional DoS attack happen on the online web site.  Reported DoS accident over the phone networks 5 KAIST | Dependable Software Lab | Direito

Contents  Introduction  Related Work  System/Attack Characterization  Mitigation Technique  Current Solution  Queue Management  Resource Provisioning  Result and Discussion  Conclusion 6 KAIST | Dependable Software Lab | Direito

System characterization(I) | Message Delivery Overview 7 KAIST | Dependable Software Lab | Direito

System characterization(I) | Message Delivery Overview – logical channel  TCH(Transfer Channel)  Carry voice traffic after call setup  CCH(Control Channel)  Transport information about the network  Assist in call setup/SMS delivery 8 KAIST | Dependable Software Lab | Direito

Attack characterization(II) | System Vulnerability – Attack Phase Step 9 KAIST | Dependable Software Lab | Direito Recognition (identification of a vulnerability) Reconnaissance (characterization of the conditions necessary to attack the vulnerability) Exploit (attacking the vulnerability) Recovery (cleanup and forensics)

KAIST | Dependable Software Lab | Direito Attack characterization(II) | System Vulnerability – Attach Phase Step  Recognition  Vul. of GSM cellular network in this paper  Problem : Bandwidth allocation in air interface(call blocking)  Shared SDCCHs Problem  Voice Communication  SMS  Reconnaissance  Using tools, an attacker can easily construct a “hit-list” of potential targets.  Exploit  Saturating sectors to their SDCCH capacity for some period of time 10 KAIST | Dependable Software Lab | Direito

Attack Characterization | Experimental Attack Characterization  Events Characterization  Deploy a detailed GSM simulator  Base scenario  Cellular deployment in the scale of metropolitan. i.e.,) Manhattan  12 SDCCHs / each of 55 sectors  No pre-SDCCH queue  Assume a Poisson distribution for the arrival of text message 11 KAIST | Dependable Software Lab | Direito

Contents  Introduction  Related Work  System/Attack Characterization  Mitigation Technique  Current Solution  Queue Management  Resource Provisioning  Result and Discussion  Conclusion 12 KAIST | Dependable Software Lab | Direito

Mitigation Technique(I) | Current Solution  Goal  Not only protect voice services from targeted SMS attacks, But also allow SMS service to continue.  Current Deployed Solution : Edge Solution  Rate-Limiting Solution  Restrict the amount of messages on each IP  Drawbacks : Spoof IP and Existence of Zombie network  Filter SMS traffic  Similar to SPAM filtering methodology  Drawback : An adversary can bypass by generating legitimate looking SMS traffic 13 KAIST | Dependable Software Lab | Direito

Mitigation Technique(II) | Queue Management  Queue Management Technique(Network-based)  Weighted Fair Queuing(WFQ)  Fair Queuing(FQ)  Separate flows into individual queues and then apportions bandwidth equally between them(Round Robin)  Drawback : small time for packet to be transferred  Weighted Fair Queue(WFQ) in this paper  To solve FQ drawback, set priority to each flow.  Voice Call has higher priority compare to SMS  Install two queue on SDCCHs for Voice Call and SMS 14 KAIST | Dependable Software Lab | Direito

Mitigation Technique(II) | Queue Management(cont.)  Weighted Random Early Detection(WRED)  Random Early Detection(RED)  Prevent queue lockout by dropping packets base on Qavg  Weighted Random Early Detection(WRED)  Determine the victims to be dropped base on packet’s priority 15 KAIST | Dependable Software Lab | Direito

Mitigation Technique(III) | Resource Provisioning  Resource Provisioning(Air Interface)  Strict Resource Provisioning(SRP)  Some subset of SDCCH is only for Voice Call  Voice Call and SMS are shared other SDCCHs.  Dynamic Resource Provisioning(DRP)  If a small number of unused TCHs could be repurposed as SDCCHs, additional bandwidth could be provided to mitigate such attack.  Drawback : increase call blocking because of TCH exhaustion  Direct Channel Allocation(DCA)  The ideal means of eliminating the competition for resource - the separation of shared mechanism.  Separate SDCCHs to only Call setup and only SMS, strictly 16 KAIST | Dependable Software Lab | Direito

Contents  Introduction  Related Work  System/Attack Characterization  Mitigation Technique  Current Solution  Queue Management  Resource Provisioning  Result and Discussion  Conclusion 17 KAIST | Dependable Software Lab | Direito

Simulation Result(I) | Queue Management Technique 18 KAIST | Dependable Software Lab | Direito  WFQ vs. WRED

KAIST | Dependable Software Lab | Direito Simulation Result(II) | Queue Management Technique 19 KAIST | Dependable Software Lab | Direito  SRP vs. DRP vs. DCA

KAIST | Dependable Software Lab | Direito Contents  Introduction  Related Work  System/Attack Characterization  Mitigation Technique  Current Solution  Queue Management  Resource Provisioning  Result and Discussion  Conclusion 20 KAIST | Dependable Software Lab | Direito

Conclusion  Vulnerability by SMS-based DOS over the phone Network  Adversaries with limited resources can cause call blocking probabilities(70%) – incapacitating a cellular network  This work provides some preliminary solutions and analysis for these vulnerabilities.  Queue Management Scheme  Resource Provisioning  Future works  Seek more general solution that address these vulnerabilities 21 KAIST | Dependable Software Lab | Direito