Thoughts About Counter-Forenics and Attacks on Logs

This morning, I read this story on ZDNet about a report from Carbon Black.  The report indicates that 72% of Carbon Black’s incident response group reported working on cases where the adversary destroyed logs.  Generally, such stats aren’t particularly insightful for a variety of reasons[1], however it should be intuitive that an adversary has a vested interest in obscuring his or her illicit activities on a compromised system.

The CIS Top 20 Critical Cyber Security Controls control number 6 touches on this point by recommending systems send logs to a central log collector, but the intention is more on log collection for the purpose of aggregation and monitoring, such as with a SIEM, rather than for tamper resistance, though that is a likely side effect.  Sending logs to a remote system is a good way to ensure proper logs exist to analyze in the wake of a breach.  Also note that, in addition to deleting locally stored logs, many adversaries will disable a system’s logging service to prevent new logs from being stored locally or sent to a log collector.

Here are a few recommendations on logging:

  1. Send system logs to a log collector that is not part of the same authentication domain as the systems generating the logs.  For example, the SIEM system(s) collecting/monitoring logs should not be members of the same active directory domain as those that generate the logs.
  2. Configure the SIEM to alert on events that indicate logging services were killed (if possible).
  3. Configure the SIEM to generate an alert after a period of inactivity from any given log source.

 

[1] I need to write a blog post on the problems with reports that are based on surveys of a population.  For now, I’d encourage you to read up on these problems yourself.  It’ll make you a better consumer and a better person.

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