DHS: Put forensic preservation ahead of enemy elimination

More information is generally better than less information.

The Department of Homeland Security has advised critical infrastructure providers to preserve data before even thinking about how to find and crush the attacker.

“While the tendency might be to first find and eliminate the intruder, unless adequate steps are taken to preserve data and prevent lateral movement, the recovery processes will not likely be successful,” says DHS’s Industrial Control System Cyber Emergency Response Team (ICS-CERT) in a new advisory note.

The advice follows its report that attacks on critical infrastructure providers had more than tripled since the two it identified in 2009, albeit off the back of a 2000 per cent increase in 'reported' security incidents.

Things that should be logged at the time of the attack include times, mitigations taken or not, whether or not device logging was enabled, and “machine names for suspected compromised equipment”.

“More information is generally better than less information,” ICS-CERT advised.

The advisory contains tips on what to do to avoid destroying forensic data in the process of protecting systems, including seeming ambiguities that might not be considered by an administrator while the organisation is under attack, such as removing an infected host from the network but not powering it down.

“When a compromised host is identified, it should be removed from the network for forensic data collection -- but not powered off.”

That means that when powering down a system, the device should be simply unplugged “rather than gracefully shutting down”.

“Forensic data can be destroyed if the operating system (OS) executes a normal shut down process,” explained ICS-CERT.

Other advice included:

  • After shutting down, capture forensic images of the host hard drives.
  • Avoid running any antivirus software “after the fact” as the antivirus scan changes critical file dates and impedes discovery and analysis of suspected malicious files and timelines.
  • Avoid making any changes to the OS or hardware, including updates and patches, as they might overwrite important information relevant to the analysis. Organisations should consult with trained forensic investigators for advice and assistance prior to implementing any recovery or forensic efforts.

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