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(Still) Exploiting TCP Timestamps Veit N. Hailperin 1 1 scip AG Hack - PowerPoint PPT Presentation

May 08, 2023 •152 likes •623 views

(Still) Exploiting TCP Timestamps Veit N. Hailperin 1 1 scip AG Hack in Paris, June 2015 Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 1 / 47 About Me Security Consultant & Researcher @ scip AG @fenceposterror

  1. (Still) Exploiting TCP Timestamps Veit N. Hailperin 1 1 scip AG Hack in Paris, June 2015 Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 1 / 47

  2. About Me Security Consultant & Researcher @ scip AG @fenceposterror Bug in the matrix Disclaimer I will use IP on the slides synonym to IP address for space reasons. Timestamps allows refer to TCP timestamps if not otherwise noted. Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 2 / 47

  3. Outline What are TCP Timestamps? 1 A History of Exploitation and Failed Remediation 2 More Fun with TCP Timestamps 3 What Now? 4 Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 3 / 47

  4. TCP Timestamps Introduced in 1992 Described in RFC1323 Extension to provide PAWS and improved RTTM A constant, strictly monotonous increasing number Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 4 / 47

  5. A TCP Timestamp Kind: 8 Length: 10 bytes +-------+-------+---------------------+---------------------+ |Kind=8 | 10 | TS Value (TSval) |TS Echo Reply (TSecr)| +-------+-------+---------------------+---------------------+ 1 1 4 4 Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 5 / 47

  6. Attack Vector - Timestamp 2001 - Uptime Calculation Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 6 / 47

  7. Attack Vector - Timestamp 2001: Uptime Calculation Timestamp != Uptime Multiple timestamps ⇒ frequency of host ⇒ timestamp & frequency ⇒ uptime Uptime related to patch level Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 7 / 47

  8. Attack Vector - Timestamp 2001: Uptime Calculation - Remediation Disable timestamps (bad idea) Randomize timestamps at boot (problems: lack of entropy, determination of initial value easy) Start each new TCP Connection with 0 (problem: still PAWS) Timestamp per IP/port pair (problem: only a question of time) More problems: Might break syn flood protection under linux Timestamp counter for each IP Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 8 / 47

  9. Attack Vector - Timestamp 2015: Uptime Calculation Still possible 1 . . . Also: timestamps observed over a longer period also lets us know their habits, e.g. when shutting down, when booting, . . . 1 It’s a tiny bit more tricky for a small group of systems Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 9 / 47

  10. Attack Vector - Timestamp 2005 - Host Identification Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 10 / 47

  11. Attack Vector - Timestamp 2005: Host Identification = ⇒ Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 11 / 47

  12. Attack Vector - Timestamp 2005: Host Identification - Remediation Randomizing/Zeroing timestamps (loss of functionality) Use a different counter for each connection and initialize with 0 (problem: PAWS) Like above but with randomized start (problem: PAWS) Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 12 / 47

  13. Attack Vector - Timestamp 2015: Host Identification Still possible 2 . . . 2 It’s a tiny bit more tricky for a small group of systems Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 13 / 47

  14. Attack Vector - Clock Skew Let’s assume we did fix the aforementioned issues, are we done? no :( (Mainly) due to physical properties (heat, fabrication, . . . ) clock isn’t exact This slight imperfection of clock can be used as identifier (clock skew) Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 14 / 47

  15. Attack Vector - Clock Skew 2005 - Host Identification Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 15 / 47

  16. Attack Vector - Clock Skew 2005: Host Identification Possible even if host/port tuple TCP timestamp solution got implemented Multiple IPs virtually hosted not possible with timestamp (because TS per OS) With clock skew not a problem, because they share hardware Interesting to track users Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 16 / 47

  17. Attack Vector - Clock Skew 2005: Host Identification - Remediation Reduce device’s clock skew (difficult!) Mask clock skew by multiplying timestamp with random value (breaks RFC) mod skewmask: Mask clock skew with constant Encrypt timestamps (breaks RFC) Table mapping between random 32-bit values and internal representation of real timestamps (breaks RFC) Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 17 / 47

  18. Attack Vector - Clock Skew 2015: Host Identification Still possible 3 . . . 3 Some honeypots try to avoid it Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 18 / 47

  19. Attack Vector - Clock Skew 2005 - Network Layout Information Gathering Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 19 / 47

  20. Attack Vector - Clock Skew 2005: Network Layout Information Gathering Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 20 / 47

  21. Attack Vector - Clock Skew 2005: Network Layout Information Gathering - Remediation Same as for host identification Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 21 / 47

  22. Attack Vector - Clock Skew 2015: Network Layout Information Gathering Still possible . . . Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 22 / 47

  23. Attack Vector - Clock Skew 2006 - Reveal Hidden Services Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 23 / 47

  24. Attack Vector - Clock Skew 2006: Reveal Hidden Services Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 24 / 47

  25. Attack Vector - Clock Skew 2006: Reveal Hidden Services - Remediation Dummy Traffic Fixed QoS for all connections ⇒ No anonymous stream affects another (problem: potential DoS if connections idle) Oven Controlled Crystal Oscillators (OCXO) Always run at maximum CPU load Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 25 / 47

  26. Attack Vector - Clock Skew 2015: Reveal Hidden Services Still possible . . . Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 26 / 47

  27. Possible Targets Users Servers Conclusion More or less everyone/everything is affected Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 27 / 47

  28. More Fun with TCP Timestamps 2015 - Reveal Active-Active Loadbalancing Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 28 / 47

  29. More Fun with TCP Timestamps 2015 Load-Balanced Check! Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 29 / 47

  30. More Fun with TCP Timestamps 2015 Load-Balanced Check! Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 30 / 47

  31. More Fun with TCP Timestamps 2007/2015 - Network Layout Information Gathering Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 31 / 47

  32. More Fun with TCP Timestamps 2015: Network Layout Information Gathering DEMO 4 4 https://github.com/luh2/timestamps Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 32 / 47

  33. More Fun with TCP Timestamps 2015: Network Layout Information Gathering Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 33 / 47

  34. More Fun with TCP Timestamps 2015: Network Layout Information Gathering Count IPs behind a NAT (if you are the receiving end of connections) (2007) Identify hosts behind a NAT (if you have multiple ports open) (2015) TCP timestamp is the same ⇒ services on same host TCP timestamp is different ⇒ services on different hosts Some ports answer with no timestamp ⇒ Can’t tell Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 34 / 47

  35. More Fun with TCP Timestamps 2015: Network Layout Information Gathering No tool that exploits this knowledge Does someone want to write a Nmap script? Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 35 / 47

  36. More Fun with TCP Timestamps 2007/2015: Network Layout Information Gathering - Remediation Increment randomly (defeats RTTM) Rewrite timestamp on NAT device Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 36 / 47

  37. More Fun with TCP Timestamps 2015 - Improve OS Fingerprints of NAT-ed Devices Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 37 / 47

  38. More Fun with TCP Timestamps 2015 Improve OS Fingerprints Repeat: What is a OS Fingerprint? Nmap doesn’t assume aforementioned scenario, but direct fingerprinting Use knowledge which ports belong together Don’t use closed ports Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 38 / 47

  39. More Fun with TCP Timestamps 2015 Improve Fingerprints! DEMO Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 39 / 47

  40. Proposed Solutions Terminate TCP connection at firewall Veit N. Hailperin (scip AG) (Still) Exploiting TCP Timestamps HiP 2015 40 / 47

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