Google Cloud GCE instance startup script added or modified

gcp

Classification:

attack

Tactic:

TA0003-persistence

Technique:

T1098-account-manipulation

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Goal

Detect when an attempt to add or modify a startup script to the GCE instance metadata occurs.

Strategy

This rule monitors Google Cloud Audit Logs to determine when an attempt to add or modify a start up script to the GCE instance metadata has occurred. A malicious actor who has already gained initial access may try to preserve access to GCE instances by adding a custom startup script to the instance metadata.

Note: This rule triggers with a Medium severity when this activity originates from an anonymizing proxy.

Triage and response

  1. Reach out to the user or owner of the service account to determine if this action is legitimate.
  2. If the action is legitimate, consider including the IP address or ASN in a suppression list. See this article on Best practices for creating detection rules with Datadog Cloud SIEM for more information.
  3. Otherwise, use the Cloud SIEM - IP Investigation dashboard to see if the IP address: {{@network.client.ip}} has taken other actions.
  4. If the results of the triage indicate that a malicious actor has taken the action, begin your company’s Incident Response process and investigate.

Changelog

  • 25 September 2024 - Updated query to replace attribute @threat_intel.results.category:anonymizer.