1. 1 Protecting SIP Against DoS An Architectural Approach

2. 2 Motivation ► SIP implementations vulnerable to DoS ► Current solutions placed near destination  But these cannot cope with large attacks ► Need an architectural approach  Detect attack at destination  Block attack close to its sources

3. 3 Basic Architecture ISP A Internet SIP FILTER SIP AGENTS SIP FILTER Legacy ISP B ISP B ISP D SIP FILTER SIP AGENTS Detect attack A filter request A

4. 4 Basic Architecture: Detailed View C1 ISP A (SRC) Internet ISP B (DST) ISF C2 C3 PAPA C = SIP UA ISF = Ingress SIP filter ESF = Egress SIP filter R = SIP registrar P = SIP proxy RARA PAPA RARA ESF C4 Filter Request, send to ISF@domain

5. 5 Basic Architecture: No Proxies C1 ISP A (SRC) Internet ISP B (DST) ISF C2 C3 PAPA RARA PAPA RARA ESF C4

6. 6 Basic Architecture: One Proxy C1 ISP A (SRC) Internet ISP B (DST) ISF C2 C3 PAPA RARA PAPA RARA ESF C4

7. 7 Basic Architecture: Two Proxies C1 ISP A (SRC) Internet ISP B (DST) ISF C2 C3 PAPA RARA PAPA RARA ESF C4

8. 8 SIP ID-spoofing Prevention: Intra-Domain C1 ISP ISF R SIP ID: johnp IP: 10.0.0.100 MAC: 00:00:00:00:00:00 C2 SIP ID: jackh IP: 10.0.0.101 MAC: 00:00:00:00:00:01 C3 SIP ID: eve IP: 10.0.0.102 MAC: 00:00:00:00:00:02 Database:.100 / :00:00.101 / :00:01.102 / :00:02 Database:.100 / johnp.101 / jackh.102 / jillm INTERNET.100 = johnp? YES.100 = eve? NO!

9. 9 SIP ID-spoofing Prevention: Inter-Domain C1 ISP A (SRC) Internet ISP B (DST) ISF C2 C3 PAPA RARA PAPA RARA ESF C4 TLS tunnel ► ESF trusts packets came from ISF (TSL tunnel) ► ESF trusts ISF to ingress filter ► So, ESF can tell packets came from C1, C2 or C3

10. 10 Filtering Protocol ► Detector at destination triggers filter request ► Need to know which SF to send request to  Wait until next packet, record TLS endpoint ► Need to authenticate requests  TLS tunnel takes care of this

11. 11 Attack Detection ► Either at source or destination domain  Destination ► Can detect even very distributed attacks ► State-holding attacks on proxies  Source ► Can prevent spoof-based attacks ► Can detect flooding clients, prevent attack

12. 12 Additional Slides

13. 13 Attacks Prevented by Authentication Mechanism ► BYE attack ► CANCEL attack ► RE-INVITE / UPDATE attacks ► REFER attack (don’t accept from non-tunneled referrers) ► Route-record spoofing (don’t accept from non-tunneled) ► REDIRECT server impersonation, moved permanently ► Reflection, fake Route, Via or Request-URI ► Reflection, spoofed INVITE ► State-holding attack, INVITEs with spoofed SIP IDs

14. 14 Attacks Prevented by Source-Domain Filtering ► Registrar attacks  Flooding  Guessing login/password via brute-force  De-registering entries  Amplification attack, get all current registrations  SQL injection attacks  Registering too many IDs, amp attacks through forking ► Parser attacks  Large header/body  Mismatched Content-Length header to actual length  Malicious re-arrangement of fundamental headers

15. 15 Attacks Prevented by Source-Domain Filtering (ctnd) ► Flooding attacks  SIP Invites  State-holding for proxies, too many sessions ► Proxy attacks  Force look-up of fake DNS names, black-list  Loops through Via header

16. 16 Attacks Prevented by Destination-Domain Filtering ► Distributed Flooding attacks ► State-holding attacks on proxies (black list?)  INVITE to unresponsive TCP port  INVITE to co-operating but unresponsive node  Colluding node, too many open sessions

17. 17 Possible Extensions ► Captchas ► Scoring (and its authentication) ► Logging of filtered calls?

18. 18 Bibliography ► RFC3261, RFC2543, RFC4474 ► VOIP Intrusion Detection Through Interacting Protocol State Machines ► VoIP Honeypot Architecture ► Understanding SIP ► VoIP Security and Privacy Threat Taxonomy ► Survey of Security Vulnerabilities in SIP

19. 19 ISP C1 C2 C3 SF Basic Architecture: Deployment P Re INTERNET SIP traffic Ro Non-SIP traffic Ro SIP IN traffic: to SF Filter only IN traffic to SF

20. 20 NATs: Enterprise Scenario C1 ISP A (SRC) Internet ISP B (DST) ISF C2 C3 PAPA RARA PAPA RARA ESF C4 Filter Request, send to ISF@domain NAT

21. 21 NATs: End-Customer Scenario C1 ISP A ISF C2 C3 PAPA RARA NAT HOME Internet ► ISF can only ingress filter for NAT’s MAC ► R has multiple SIP IDs for NAT’s IP ► Filter: C1@ISPA ► C2 can still DoS C1, but this is local problem 128.16.6.8 C1 : 128.16.6.8 C2 : 128.16.6.8 C3 : 128.16.6.8