gcp_identity_low_and_medium_severity_alert_escalation

rule gcp_identity_low_and_medium_severity_alert_escalation {

  meta:
    author = "Mo Mohajerani"
    description = "Detects when a Google Cloud identity experiences a low severity event followed by medium severity event within 24 hours."
    rule_name = "Google Cloud identity low and medium alert escalation"
    rule_id = "mr_fafc6c00-aedb-4664-ae1a-5a48f3a7534d"
    type = "Alert"
    platform = "GCP"
    data_source = "Security Command Center Threat"
    mitre_attack_tactic = "Defense Evasion, Persistence, Privilege Escalation, Initial Access"
    mitre_attack_technique = "Valid Accounts"
    severity = "High"
    priority = "High"

  events:
    // Low severity alert triggered in SCC
    $low_severity.metadata.product_name = "Security Command Center"
    $low_severity.security_result[0].severity = "LOW"
    $low_severity.principal.user.email_addresses = $user_email
    // Medium severity alert triggered in SCC
    $medium_severity.metadata.product_name = "Security Command Center"
    $medium_severity.security_result[0].severity = "MEDIUM"
    $medium_severity.principal.user.email_addresses = $user_email
    // Enforces the sequence of events, ensuring the low severity event(s) triggered prior to the medium severity event(s)
    $low_severity.metadata.event_timestamp.seconds < $medium_severity.metadata.event_timestamp.seconds

  match:
    $user_email over 24h

  outcome:
    // Risk score is increased when the suspicious identity has been accessed from unexpected locations
    // This logic can be customized based on your organization's environment and normal activity
    $risk_score = max(80 + if($low_severity.principal.location.country_or_region != "Germany", 10))
    $mitre_attack_tactic = "Defense Evasion, Persistence, Privilege Escalation, Initial Access"
    $mitre_attack_technique = "Valid Accounts"
    $mitre_attack_technique_id = "T1078"
    $security_category = array_distinct($medium_severity.security_result.category)
    $security_category_details = array_distinct($medium_severity.security_result.category_details)
    $security_summary = array_distinct($medium_severity.security_result.summary)
    $affected_identity = array_distinct($medium_severity.principal.user.userid)
    $principal_ip_country = array_distinct($medium_severity.principal.ip_geo_artifact.location.country_or_region)
    $principal_ip_state = array_distinct($medium_severity.principal.ip_geo_artifact.location.state)
    $event_count_low = count_distinct($low_severity.metadata.id)
    $principal_user_display_name = array_distinct($medium_severity.principal.user.user_display_name)

  condition:
    $low_severity and $medium_severity
}