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Elastic Docs ›Elastic Security [8.19] ›Downloadable rule update v8.19.21

AWS Rare Source AS Organization Activity

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IMPORTANT: This documentation is no longer updated. Refer to Elastic's version policy and the latest documentation.

AWS Rare Source AS Organization Activity

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Surfaces an AWS identity whose successful API traffic is dominated by a small set of large cloud-provider source AS organization labels, yet also shows a very small share of traffic from other AS organization names—including at least one sensitive control-plane, credential, storage, or model-invocation action on that uncommon network path with recent activity from the uncommon path. The intent is to highlight disproportionate “baseline” cloud egress versus sparse use from rarer networks on the same principal, a shape that can appear when automation or CI credentials are reused or pivoted outside their usual hosted-cloud footprint.

Rule type: esql

Rule indices: None

Severity: high

Risk score: 73

Runs every: 1h

Searches indices from: now-7d (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Cloud
  • Data Source: AWS
  • Data Source: Amazon Web Services
  • Data Source: AWS CloudTrail
  • Use Case: Threat Detection
  • Tactic: Initial Access
  • Resources: Investigation Guide

Version: 1

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

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Triage and analysis

Investigating AWS Rare Source AS Organization Activity After High Cloud-Provider Volume

The rule aggregates roughly seven days of successful CloudTrail per user.name and aws.cloudtrail.user_identity.type. It expects a high count of events whose GeoIP AS organization matches a short allowlist of large cloud/SaaS providers, at least one event from a different AS organization, a low ratio of uncommon-network events to all events, few distinct uncommon AS labels, and recent uncommon-network timestamps. It further requires at least one sensitive API from an uncommon network (see query event.action list).

Possible investigation steps

  • Compare Esql.src_asn_values to Esql.user_agent_values and map each source.ip (from raw CloudTrail) to expected admin paths, pipelines, or offices.
  • Pivot on user.name and aws.cloudtrail.user_identity.access_key_id (from underlying events) for IAM, STS, S3, and Secrets Manager activity around Esql.most_recent_low_asn_day.
  • Confirm whether the identity is meant for automation only; if so, rare human ISP ASNs warrant higher scrutiny.
  • Review Esql.untrusted_suspicious_actions for the mix of discovery versus privilege-changing APIs.

False positive analysis

  • Threshold sensitivity: Raise Esql.trusted_cloud_event_count or Lower Esql.rare_asn_ratio and Esql.untrusted_event_count if legitimate rare-ASN noise persists.
  • MongoDB / other allowlist labels: Extend is_trusted_cloud if your approved automation consistently appears under another legal-entity string.

Response and remediation

  • If abuse is plausible: rotate credentials for the principal, enforce OIDC or short-lived keys for automation, and tighten IAM and data-plane permissions.

Additional information

Rule query

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FROM logs-aws.cloudtrail-*
| WHERE event.dataset == "aws.cloudtrail"
  AND event.outcome == "success"
  AND source.as.organization.name IS NOT NULL
  AND user.name IS NOT NULL

| EVAL is_trusted_cloud = CASE(
    source.as.organization.name LIKE "Amazon*" OR
    source.as.organization.name == "Google LLC" OR
    source.as.organization.name == "Microsoft Corporation" OR
	source.as.organization.name == "MongoDB, Inc.",
    true, false
  )

| EVAL is_suspicious_action = CASE(
    event.action IN (
      "GetCallerIdentity", "GetAccountSummary", "ListAccountAliases",
      "GetSecretValue", "ListSecrets", "DescribeSecret",
      "GetParameter", "GetParameters", "GetParametersByPath",
      "AssumeRole", "AssumeRoleWithWebIdentity", "AssumeRoleWithSAML",
      "AttachUserPolicy", "AttachRolePolicy",
      "PutUserPolicy", "PutRolePolicy",
      "CreateAccessKey", "UpdateAccessKey",
      "CreateUser", "CreateLoginProfile",
      "UpdateLoginProfile", "AddUserToGroup",
      "GetObject", "ListBuckets", "ListObjects", "ListObjectsV2",
      "InvokeModel", "InvokeModelWithResponseStream", "Converse"
    ), true, false
  )

// Single aggregation — full event count preserved for ratio logic
// suspicious action tracking is additive on top
| STATS
    Esql.total_events_all_asns = COUNT(*),
    Esql.count_distinct_asns = COUNT_DISTINCT(source.as.organization.name),
    Esql.src_asn_values = VALUES(source.as.organization.name),
	Esql.user_agent_values = VALUES(user_agent.original),
	Esql.related_users = VALUES(user.changes.name),
	Esql.source_ip_values = VALUES(source.address),
    Esql.has_trusted_cloud_asn = MAX(is_trusted_cloud),
    Esql.trusted_cloud_event_count = SUM(CASE(is_trusted_cloud == true, 1, 0)),
    Esql.untrusted_event_count = SUM(CASE(is_trusted_cloud == false, 1, 0)),
    // Suspicious action visibility from untrusted ASNs — informational only, not a filter
    Esql.untrusted_suspicious_count  = SUM(CASE(
        is_trusted_cloud == false AND is_suspicious_action == true, 1, 0
      )),
    Esql.untrusted_suspicious_actions = VALUES(CASE(
        is_trusted_cloud == false AND is_suspicious_action == true,
        event.action, null
      )),
    Esql.most_recent_low_asn_day   = MAX(CASE(
        is_trusted_cloud == false, @timestamp, null
      ))
    BY user.name, aws.cloudtrail.user_identity.type

| EVAL Esql.rare_asn_ratio = TO_DOUBLE(Esql.untrusted_event_count) / TO_DOUBLE(Esql.total_events_all_asns),
       Esql.unique_action_from_untrusted_asn = MV_COUNT(Esql.untrusted_suspicious_actions)

// Detection thresholds — unchanged, full event counts drive the logic
| WHERE Esql.has_trusted_cloud_asn == true
  AND Esql.untrusted_event_count >= 1
  AND Esql.trusted_cloud_event_count >= 100
  AND Esql.rare_asn_ratio <= 0.01
  AND Esql.unique_action_from_untrusted_asn >= 2
  AND Esql.count_distinct_asns <= 5
  AND Esql.most_recent_low_asn_day >= NOW() - 1 hour

| KEEP user.name,
       aws.cloudtrail.user_identity.type,
       Esql.*

Framework: MITRE ATT&CKTM

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