What is Stuxnet?

What did Stuxnet do?

How Stuxnet works: The air gap myth

  • Attackers lack sufficient knowledge and incentive to target ICS and SCADA systems.
  • Cyber security is important mostly for IT and enterprise systems.
  • Proven security strategies don’t apply to the majority of operational technology systems because the risk of disruption is too high in OT.

How did Stuxnet spread?

  • Noisily pivoted through the environment via Windows Remote Procedure Calls (RPC), Server Message Block (SMB), and MS SQL protocols.
  • Leveraged a Windows Shortcut (.lnk) zero-day vulnerability that thwarted the disabling USB and removable media auto-play.
  • Used stolen code signing certificates to make its malicious payloads appear as legitimate drivers that were recognized by the operating system and ignored by anti-virus and policy enforcement controls.
  • Leveraged vulnerabilities in Windows print spooling network services (usually on by default) hosts where infection was not possible through RPC/SMB/SQL and USB insertion. This included privilege escalation.
  • Possessed the ability to leverage the OPC protocol to traverse segments.
  • Infected Siemens STEP7 project files, replacing legitimate STEP7 DLLs with modified malicious ones, and using hard-coded credentials to log in to the Siemens WinCC SCADA database to identify specific targets.
  • Rendered itself dormant if appropriate criteria were not met.

How to prevent Stuxnet

  • Reliance on an air gap as a stand-alone security measure was an absolute failure.
  • Traditional anti-virus would not have found this type of malware.
  • Updated host OS may have helped with some of the exploits, but again, unlikely given the attackers’ skill level.
  • Application whitelisting and host integrity checking probably would have detected the replaced STEP7 DLLs and altered project files.
  • Strict removable media policies and enforcement (potentially even hot glue) could have prevented an initial infection or, at least, made it much harder.
  • Sufficient host hardening to include disabling unnecessary services like the Windows printer spooling service would have made lateral movement more difficult.
  • Sufficient network segmentation might have stopped the attackers from pivoting across the environment while better monitoring might have alerted defenders to anomalous traffic.
  • Diligent application of security policy could have isolated and contained the malware as it beaconed across network zones and layers where it did not belong.
  • Most importantly, better-trained resources and appropriate out-of-band (OOB) monitoring for anomalies within the centrifuge halls could have contained the damage early on in the attack.



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