Voice over IP (VoIP) security

1. Voice over IP (VoIP) security

2. Introduction • Voice over IP and IP telephony • Network convergence • Telephone and IT • PoE (Power over Ethernet) • Mobility and Roaming • Telco • Switched -> Packet (IP) • Closed world -> Open world • Security and privacy • IPhreakers • VoIP vs 3G

3. Architecture: protocols • Signaling • User location • Session • Setup • Negotiation • Modification • Closing • Transport • Encoding, transport, etc.

4. Architecture: protocols • SIP • IETF - 5060/5061 (TLS) - “HTTP-like, all in one” • Proprietary extensions • Protocol becoming an architecture • “End-to-end” (between IP PBX) • Inter-AS MPLS VPNs • Transitive trust • IM extensions (SIMPLE) • H.323 • Protocol family • H.235 (security), Q.931+H.245 (management), RTP, CODECs, etc. • ASN.1

5. Architecture: protocols • RTP (Real Time Protocol) • 5004/udp • RTCP • No QoS/bandwidth management • Packet reordering • CODECs • old: G.711 (PSTN/POTS - 64Kb/s) • current: G.729 (8Kb/s)

6. Architecture: systems • Systems • SIP Proxy • Call Manager/IP PBX • User management and reporting (HTTP, etc) • H.323: GK (GateKeeper) • Authentication server (Radius) • Billing servers (CDR/billing) • DNS, TFTP, DHCP servers

7. Architecture: systems • Voice Gateway (IP-PSTN) • Gateway Control Protocols • Signaling: SS7 interface • Media Gateway Controller • Controls the MG (Megaco/H.248) • SIP interface • Signaling Gateway • Interface between MGC and SS7 • SCTP - ISUP, Q.931 • Transport • Media Gateway: audio conversion

8. Architecture: firewall/VPN • Firewall • “Non-stateful” filtering • “Stateful” filtering • Application layer filtering (ALGs) • NAT / “firewall piercing” • (H.323 : 2xTCP, 4x dynamic UDP - 1719,1720) • (SIP : 5060/udp) • Encrypted VPN • SSL/TLS • IPsec • Where to encrypt (LAN-LAN, phone-phone, etc)?

9. VOIP Threats • Denial of Service • ICMP Flood • IP Spoofing • Port Scans • Land Attack • IP Source Route • Evasdropping or recording • In VOIP eavesdropping is a type of an attack, if an attacker able to eavesdropp a communication. Then he can launch different type of an attack like Man in the Middle attack etc. • Call Hijacking and Spoofing • Call Redirection • Voice SPAM (Vishing, Mailbox Stuffing, Unsolicited Calling) • Voicemail Hacking

10. VOIP Attacks • Signaling Layer Attacks • SIP Registration Hijacking • Impersonating a Server • SIP Message Modification • SIP Cancel / SIP BYE attack • SIP DOS attack • Media Layer Attacks • Eavesdropping • RTP insertion attack • SSRC collision attacks

11. Signaling Layer Attacks • SIP Registration attack • Attacker impersonates a valid UA to a registrar himself as a valid user agent. So attacker can recieve calls for a legitmate user. • Impersonating a Server • When an attacker impersonates a remote server and user agent request are served by the attacker machine. • SIP Message Modification • If an attacker launches a man in the middle attack and modify a message. Then attacker could lead the caller to connect to malicious system. • SIP CANCEL / SIP BYE • SIP Denial of Service • In SIP attacker creates a bogus request that contained a fake IP address and Via field in the SIP header contains the identity of the target host.

12. Media Layer Attacks • Eavesdropping • SSRC collision • If an attacker eavesdropp the conversation and uses one’s peer SSRC to send RTP packet to other peer, it causes to terminate a session.

13. Security Solutions • Two types of security solutions • End-to-End security • In SIP end points can ensure end-to-end security to those messages which proxy does not read, like SDP messages could be protectedusingS/MIME. • Media is transferred directly, so end-to-end security is achieved by SRTP. • Hop-by-hop security • TLS, IPSec • TLS provide transport layer security over TCP. Normally SIP URI is in the form of sip:abc@example.com, but if we are using TLS then SIP URI will be sips:abc@example.com and signaling must be send encrypted.

14. Authentication • Authentication means to identify a person. • If we take SIP as signaling protocol in VOIP, it defines two mechanisms for authentication • HTTP digest authentication • S/MIME • HTTP Digest Authentication • HTTP digests mechanisms used between users to proxies, users to users but not between proxies to proxies. • S/MIME • S/MIME uses X.509 certificates to authenticate end users in the same way that web browsers use them.

15. Media Encryption • In VOIP media is send directly between users using RTP. Encryption of media is achieved by • IPSec • Secure RTP (SRTP) • It provides a framework for encryption and message authentication of RTP and RTCP. • Cipher Algorithum: AES • Authenitcation is an optional feature. • SRTP uses Security Description for Media Streams (SDES) algorithum to negotiate session keys in SDP. • MIKKEY • Mikkey provides its own authentication and integrity mechanisim. • Mikkey messages carried in a SDP with a=key-mgmt attritbute.

16. There are Specialized Hacking Tools • SIPScan - enumerate SIP interfaces • TFTPBrute - TFTP directory attacking • UDP and RTP Flooder - DoS tools • hping2 – TCP session flooding • Registration Hijacker - tool to take over H.323 session • SIVUS - SIP authentication and registration auditor • Vomit - RTP Playback • VOIP HOPPER – IP Phone mimicing tool • Dsniff- various utilitarian tools (macof and arpspoof) • Wireshark (Ethereal) / tcpdump - packet capture and protocol analysis

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