Reported this week, 'Skeleton Key malware that bypasses AD Authentication'. So what do you need to know to protect your AD Servers from this and other attacks?

“Dell SecureWorks Counter Threat Unit (TM) (CTU) researchers discovered malware that bypasses authentication on Active Directory (AD) systems that implement single-factor (password only) authentication. Threat actors can use a password of their choosing to authenticate as any user. This malware was given the name "Skeleton Key."

Fortunately, the nature of the malware is relatively straightforward to defend against by operating good security best practices.

SecureWorks list a series of DLL files that would need to be copied to the Domain Controller for Skeleton Key to be effective. These include

  • ole.dll
  • ole64.dll
  • msuta64.dll

Crucially, the research includes suggested deployment steps

“Use valid domain administrator credentials to copy the Skeleton Key DLL to C:\WINDOWS\system32\ on the target domain controllers”

This means that the malware would either need to be deployed using hijacked Domain Admin credentials or as an Insider Attack (malicious employee with Admin rights)

Takeaway points to mitigate this threat

  • Do you run regular (ideally continuous, real-time) File Integrity Monitoring checks to detect new or changed system files? Zero-day malware can comfortably side-step AV defenses, and an Insider with Admin rights will bypass any IPS protection or Sandbox technology.
  • Does your password policy age sufficiently frequently so that passwords regularly become redundant? It is important to ensure ‘leavers’ rights are removed promptly to prevent ex-employees retaining access rights. This should be a standard dimension of a hardened build standard
  • Finally, are Domain Admin accounts regularly reviewed and any change of privilege or new account creations monitored? (should be a standard SIEM or Logging requirement to monitor AD activity)

Its a good example of why layered security defenses are needed, and why a combination of technology and procedures are necessary. Put another way, this is why all security, governance and regulatory compliance standards are always so detailed and complex.


More details of the Dell SecureWorks research are here



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