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Policy Analysis Using Margrave

Policy Analysis Using Margrave. Shriram Krishnamurthi Brown University. 1. 2. ACL for External firewall: 1: DENY if: ifc=fw1_dmz, ipdest in blacklist 2: DENY if: ifc=fw1_ext, ipsrc in blacklist 3: DENY if: ifc=fw1_dmz, portdest=telnet

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Policy Analysis Using Margrave

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  1. Policy AnalysisUsing Margrave Shriram KrishnamurthiBrown University 1

  2. 2

  3. ACL for External firewall: 1: DENY if: ifc=fw1_dmz, ipdest in blacklist 2: DENY if: ifc=fw1_ext, ipsrc in blacklist 3: DENY if: ifc=fw1_dmz, portdest=telnet 4: ACCEPT if: ifc=fw1_ext, ipdest=mailserver, portdest=smtp, proto=tcp 5: ACCEPT if: ifc=fw1_ext, ipdest=webserver, portdest=http, proto=tcp 6: ACCEPT if: ifc=fw1_dmz, ipdest=any outside, portdest=http, proto=tcp, ipsrc=manager 7: DROP otherwise

  4. employees contractors manager DMZ int dmz dmz ext

  5. tcp www blacklist blacklist telnet tcp smtp tcp www

  6. tcp www tcp  smtp tcp smtp ipsrc fw2_static

  7. Problem The manager can’t connect to the Web.

  8. When can a connection from the manager’s PC be denied if it’s • to port 80 (www) • over TCP • to any machine?

  9.  p . p.dstprt = www  p.proto = TCP  p.ipdest  outIPs  p.ipsrc = manager  Int.ACL denies p   p’ . Int.NAT translates p to p’  p’.dstprt = p.dstprt  p’.proto = p.proto  p’.ipdest = p.ipdest  Ext.ACL denies p’

  10. When can a connection from the manager’s PC be denied if it’s • to port 80 (www) • over TCP • to any machine? • Always: • Int’s ACL accepts the packet via rule 4. • Int’s NAT applies to the packet. • Ext’s ACL denies the post-NAT packet via rule 7.

  11. Margrave Design Principles

  12. Property-Free Analysis(e.g., Change Impact)

  13. thepolicy  ⊦ P • Does • its property? • satisfy

  14. ⊦ P Can people state them? Are they good enough? 14

  15. ACL for External firewall: 1: DENY if: ifc=fw1_dmz, ipdest in blacklist 2: DENY if: ifc=fw1_ext, ipsrc in blacklist 3: DENY if: ifc=fw1_dmz, portdest=telnet 4: ACCEPT if: ifc=fw1_ext, ipdest=mailserver, portdest=smtp, proto=tcp 5: ACCEPT if: ifc=fw1_ext, ipdest=webserver, portdest=http, proto=tcp 6: ACCEPT if: ifc=fw1_dmz, ipdest=any outside, portdest=http, proto=tcp, ipsrc=managerfw2_static 7: DROP otherwise

  16.  p . Int.ACL accepts p   p’ . Int.NAT translates p to p’  p’.dstprt = p.dstprt  p’.proto = p.proto  p’.ipdest = p.ipdest  ((Ext.ACL denies p’  Ext.ACLNew accepts p’)  (Ext.ACL accepts p’  Ext.ACLNew denies p’))

  17. p.entry-interface = fw2_int p.ipsrc = manager p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp p.entry-interface = fw2_int p.ipsrc = contractor p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp p.entry-interface = fw2_int p.ipsrc = employee p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp

  18. p.entry-interface = fw2_int p.ipsrc = contractor p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp p.entry-interface = fw2_int p.ipsrc = employee p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp Defining Difference A function mappingrequests tochanges in outcome Deny to Permit Permit to Deny  packets

  19. Change as a First-Class Entity • Restrict changes to External Firewall View • Which machines lost privileges? Query • Confirm no machines gained privileges Verification

  20. Configuration checking Refactoring testing ? “What if” questions Upgrade checking Finding hotspots Mutationtesting 20

  21. Scenario-Based Output p.entry-interface = fw2_int p.ipsrc = contractor p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp p.entry-interface = fw2_int p.ipsrc = employee p.ipdest in outIPs p.srcprt = any p.dstprt = www p.protocol = tcp

  22. Exhaustive Answers (in Some (Useful) Cases) Bernays-Schönfinkel-Ramsey  +  overloading (subtyping) and empty sorts

  23. Minimality

  24. Multi-Lingual Support Datalog-based intermediate language

  25. Margrave Supports… • Most of XACML 1.0 and 2.0 • Cisco IOS: • ACL: standard and extended • NAT: static; dynamic: ACL-based, map-based • routing: static and policy-based • limited: BGP announcements and VPN endpoints • Amazon Access Policy Language (in SQS) • Hypervisor, based on sHype (IBM)

  26. How SDNs Change Things Global view of Configuration and State: Current networks: hard SDNs: easy (But you already know all that.)

  27. Principles Recap Property-free analysis Change-impact w/ first-class changes Scenario-based output Exhaustive answers (where possible) Minimality Multi-lingual support

  28. Dan Dougherty [WPI] • Kathi Fisler [WPI] • Tim Nelson [WPI] • Alums: • Chris Barratt [Brown ScM  BEA] • Leo Meyerovich [Brown u.g.  Berkeley] • Michael Tschantz [Brown u.g.  CMU] http://www.margrave-tool.org/

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