detection-rules
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Kubernetes Potential Endpoint Permission Enumeration Attempt by Anonymous User Detected

This rule detects potential endpoint enumeration attempts by an anonymous user. An anonymous user is a user that is not authenticated or authorized to access the Kubernetes API server. By looking for a series of failed API requests, on multiple endpoints, and a limited number of documents, this rule can detect automated permission enumeration attempts. This behavior is uncommon for regular Kubernetes clusters.

Rule type: esql
Rule indices:

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: ``
Maximum alerts per execution: 100
References:

Tags:

  • Data Source: Kubernetes
  • Domain: Kubernetes
  • Use Case: Threat Detection
  • Tactic: Discovery

Version: 1
Rule authors:

  • Elastic

Rule license: Elastic License v2

from logs-kubernetes.audit_logs-* metadata _id, _index, _version
| where (
    kubernetes.audit.user.username in ("system:anonymous", "system:unauthenticated") or
    kubernetes.audit.user.username is null or
    kubernetes.audit.user.username == ""
  ) and
  kubernetes.audit.level in ("RequestResponse", "ResponseComplete", "Request")

| eval Esql.decision = `kubernetes.audit.annotations.authorization_k8s_io/decision`
| eval Esql.code = kubernetes.audit.responseStatus.code

| eval Esql.outcome = case(
    Esql.decision == "allow", "authz_allow",
    Esql.decision == "forbid", "authz_forbid",

    // fallback: infer from status when decision is missing
    Esql.code in (401, 403), "authn_authz_failed",
    (Esql.code >= 200 and Esql.code < 300), "success",
    Esql.code == 404, "not_found",
    Esql.code is null, "unknown",
    true, "other_error"
  )

| stats
    Esql.document_count = count(),

    Esql.authz_allow_count = sum(case(Esql.outcome == "authz_allow", 1, 0)),
    Esql.authz_forbid_count = sum(case(Esql.outcome == "authz_forbid", 1, 0)),

    Esql.status_fail_count = sum(case(Esql.outcome == "authn_authz_failed", 1, 0)),
    Esql.success_count = sum(case(Esql.outcome == "success", 1, 0)),
    Esql.not_found_count = sum(case(Esql.outcome == "not_found", 1, 0)),
    Esql.other_error_count = sum(case(Esql.outcome == "other_error", 1, 0)),
    Esql.unknown_count = sum(case(Esql.outcome == "unknown", 1, 0)),

    Esql.kubernetes_audit_verb_count_distinct = count_distinct(kubernetes.audit.verb),
    Esql.kubernetes_audit_requestURI_count_distinct = count_distinct(kubernetes.audit.requestURI),
    Esql.kubernetes_audit_objectRef_resource_count_distinct = count_distinct(kubernetes.audit.objectRef.resource),

    Esql.kubernetes_audit_outcome_values = values(Esql.outcome),
    Esql.kubernetes_audit_decision_values = values(Esql.decision),
    Esql.kubernetes_audit_responseStatus_code_values = values(Esql.code),
    Esql.kubernetes_audit_responseStatus_message_values = values(kubernetes.audit.responseStatus.message),

    Esql.kubernetes_audit_verb_values = values(kubernetes.audit.verb),
    Esql.kubernetes_audit_objectRef_resource_values = values(kubernetes.audit.objectRef.resource),
    Esql.kubernetes_audit_objectRef_namespace_values = values(kubernetes.audit.objectRef.namespace),
    Esql.kubernetes_audit_user_username_values = values(kubernetes.audit.user.username),
    Esql.kubernetes_audit_user_groups_values = values(kubernetes.audit.user.groups),
    Esql.kubernetes_audit_requestURI_values = values(kubernetes.audit.requestURI),
    Esql.data_stream_namespace_values = values(data_stream.namespace)

  BY kubernetes.audit.sourceIPs, kubernetes.audit.userAgent

| where
    Esql.kubernetes_audit_requestURI_count_distinct > 5 and
    Esql.kubernetes_audit_objectRef_resource_count_distinct > 3 and
    Esql.document_count < 50 and
    (Esql.authz_forbid_count >= 1 or Esql.status_fail_count >= 1 or Esql.not_found_count >= 3)

| keep Esql.*, kubernetes.audit.sourceIPs, kubernetes.audit.userAgent

Framework: MITRE ATT&CK