Protecting Your DNP3 Networks


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Your SCADA system has a DNP3 vulnerability, now what? I shortly summarize the DNP3 vulnerabilities (and other ICS protocols too). Then I focus on the different mitigations that an ICS owner can do to mitigate these types of protocol implementation vulnerabilities even if there is no patch or patches can't be installed.

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Protecting Your DNP3 Networks

  1. 1. Chris Sistrunk, PE Sr. Consultant Mandiant
  2. 2. Let’s assume that your SCADA device has a faulty DNP3 stack…
  3. 3. “Crain and Sistrunk have discovered a boatload of ICS vulnerabilities over the years” DNPtha-reeeeeee
  4. 4. Let’s take a step back and ask some questions:  What’s the risk if this device is compromised? ◦ Probability * Impact = Risk ◦ Check out my RTU risk score pres from S4x13  What is the device talking to?  Is it DNP3 serial or IP…or both?  Is the physical security sufficient?  Will you be called at 2AM?
  5. 5. The answers to the questions tell you that you have to do something to protect the device(s)  What types of mitigations exist?  Which ones will you use? ◦ Defense in depth – more than one! ◦ Belt and suspenders!  When will they be deployed? ◦ The sooner the better!
  6. 6.  Software/firmware patches/device upgrades  Robust device and master configurations  Robust IP network configurations  DNP3-aware network tools  Proper physical security  Employee awareness  Secure coding and SDL for Vendors
  7. 7. NERC/CIP?
  8. 8.  If there is a software or firmware patch or hardware upgrade that’s out there that fixes a known DNP3 vulnerability…GO GET IT  Properly test it before you roll it out  If you’re not used to patching your SCADA system, please work with your vendors to do this to minimize downtime
  9. 9.  USE DNP3-SA! (application layer security) ◦ Correct master only talks to the correct RTU ◦ But it won’t protect against all “bugs”  Disable unused serial and network ports  Use a possible workaround (ex: auto restart)  Check the default settings ◦ DNP3 or other protocols may be factory configured ◦ If not used, disable them! ◦ DNP3 devices are on SHODAN  Many appear to have the same congfigurations
  10. 10.  When possible, DISABLE functions that aren’t required in your production systems ◦ Cold and/or Warm Restarts (FC 13 & 14) ◦ Start/Stop Application (FC 17 & 18) ◦ Save Configuration (FC 19) old Activate Configuration (FC 31) new ◦ Open, Close, Delete, Abort File (FC 25, 26, 27, 30)  If you can’t disable these, use IDS/IPS or DPI Firewalls to prevent unwanted DNP3 traffic
  11. 11.  Segment your SCADA WAN ◦ Routers, Firewalls, DMZs, & VLANs ◦ This can help isolate the network when needed  Understand your network! ◦ The bad guys sure will  Use encryption and authentication ◦ Use DNP3-SA and TLS ◦ Remote access VPNs, radios, etc ◦ Look at IEC 62351 standard (dovetails with SA)  No SCADA protocols on Corporate WAN
  12. 12. Examples of tools used in SCADA and Enterprise networks understand DNP3  Protocol analyzers such as Wireshark, ASE & TMW RTU Test Sets  IDS/IPS such as SNORT, Bro, McAfee ADM, and Checkpoint  Routers such as the Cisco CGR 2010  Field firewall w/ DNP3 Deep Packet Inspection ◦ Secure Crossing & Tofino (in the works)
  13. 13.  Newer enterprise security technologies can be used to help detect, respond, and contain threats on your SCADA network  Security Operations Center ◦ Security Analyst(s) using a SIEM ◦ Log aggregation ◦ Anomaly and intrusion detection ◦ Indicators of Compromise (IOCs) ◦ Full packet capture  Security Onion (Linux distro) 
  14. 14.  What is the proper amount of physical security? It depends…  If your Critical SCADA master has top physical security, but the serially-connected tiny distribution RTU does not, is that okay?  Use a lock that meets or exceeds: UL 437, ANSI 156.30 Grade A, or ASTM F883 Grade 6  Harden your external barriers  The better the defenses, the more time it buys you to respond
  15. 15. 3/8” Mesh ASTM Grade 6 These may buy you extra time to respond
  16. 16. “Thieves hit our store last night. This is how they circumvented the door alarm…” via
  17. 17.  Train your folks on ICS/SCADA security ◦ Security Conferences, several training classes available ◦ ICS-CERT ◦ GICSP Certification  Security awareness is important  Have a questioning attitude  Report suspicious computer or personal activity/incidents ◦ Who do you call? ◦ Internal hotline, supervisor, SOC, etc ◦ ICS-CERT (877-776-7585)
  18. 18.  Ask your vendors for DNP3-SA if they don’t have it or are already working on it  Require in the bids for new SCADA systems or upgrades to be tested by a 3rd party, including the DNP3 protocol stack ◦ Positive Tests: FAT/SAT ◦ Negative Tests: Fuzzing (it’s not new folks!)
  19. 19.  DNP3 isn’t a special case. Other ICS protocols will see the same fate Modbus, IEC 60870, IEC 61850, ICCP, EtherNet/IP…  You can defend your SCADA  Early testing both slave/server AND master/client sides of the protocol are important!  Compliance != Security, but the culture is important  Don’t count on the government to protect your critical systems…it’s your job