GKE Certificate Signing Request Self-Approved

[metadata]
creation_date = "2026/07/10"
integration = ["gcp"]
maturity = "production"
updated_date = "2026/07/10"

[rule]
author = ["Elastic"]
description = """
Detects when the same non-system GKE identity creates a CertificateSigningRequest (CSR) and then approves that same CSR
within five minutes, consistent with self-approval abuse. Attackers who gain CSR create and approval RBAC
can submit a certificate request and approve it themselves to obtain a long-lived client certificate without involving
cluster operators, a pattern documented in Kubernetes persistence research and adversary emulation.
"""
false_positives = [
    """
    Automation that both submits and approves CSRs in one workflow may trigger this rule. Baseline cert-manager or
    internal PKI pipelines and tune exclusions for known service accounts.
    """,
]
from = "now-11m"
language = "esql"
license = "Elastic License v2"
name = "GKE Certificate Signing Request Self-Approved"
note = """## Triage and analysis

### Investigating GKE Certificate Signing Request Self-Approved

This rule groups CSR create and approval events by `client.user.email` and normalized CSR name (`Esql.csr_name`).
GKE logs approval on subresource paths (`.../csr-name/approval`), so the query strips `/approval` suffixes before
correlating. An alert means the same identity both submitted and approved the same CSR within five minutes, a strong
indicator of manual self-approval rather than normal `system:gcp-controller-manager` auto-approval of node
certificates.

### Possible investigation steps

- Review `Esql.event_action_values` for the sequence of create followed by `approval.update`.
- Inspect `gcp.audit.request.spec.signerName` and decode `gcp.audit.request.spec.request` on create events for the
  requested identity.
- Validate whether the actor should hold both CSR create and approval permissions.
- Hunt for subsequent API activity authenticated as the minted certificate identity.

### False positive analysis

- cert-manager or internal PKI automation that creates and approves CSRs under the same service account in one workflow.
- GitOps or bootstrap tooling that submits and signs CSRs programmatically. Baseline known automation and tune exclusions
  for those principals.
- Two unrelated CSR events from the same user within five minutes should not match because the query requires at least
  one create and one approval-class action on the same normalized CSR name.

### Related rules

- GKE Certificate Signing Request API Client Signer Requested - 1e344fba-a2f7-462b-aaec-d6c8f80d5a28
- GKE Certificate Signing Request Privileged Identity Requested - 4159bec9-76ad-4cdc-a797-4a8572073bbe
- GKE Client Certificate Signing Request Created or Approved - ec67ab57-945a-4edb-84f8-1d7a51f46544

### Response and remediation

- Revoke or deny the CSR, remove approval RBAC from untrusted principals, and rotate cluster signing credentials if
  abuse is confirmed.

"""
setup = "The GCP Fleet integration with GKE audit logs enabled is required to be compatible with this rule."
references = [
    "https://kubernetes.io/docs/reference/access-authn-authz/certificate-signing-requests/",
    "https://kubernetes.io/docs/concepts/security/rbac-good-practices/",
    "https://stratus-red-team.cloud/attack-techniques/kubernetes/k8s.persistence.create-client-certificate/",
    "https://raesene.github.io/blog/2022/12/21/Kubernetes-persistence-with-Tocan-and-Teisteanas/",
    "https://www.aquasec.com/blog/kubernetes-rbac-privilige-escalation/",
]
risk_score = 73
rule_id = "e155e658-3dcd-4d27-a4e5-1d8da6704b0e"
severity = "high"
tags = [
    "Domain: Cloud",
    "Domain: Kubernetes",
    "Data Source: GCP",
    "Data Source: GCP Audit Logs",
    "Data Source: Google Cloud Platform",
    "Use Case: Threat Detection",
    "Tactic: Persistence",
    "Tactic: Privilege Escalation",
    "Resources: Investigation Guide",
]
timestamp_override = "event.ingested"
type = "esql"

query = '''
from logs-gcp.audit-* metadata _id, _index, _version
| where data_stream.dataset == "gcp.audit"
    and service.name == "k8s.io"
    and event.outcome == "success"
    and event.action in (
      "io.k8s.certificates.v1.certificatesigningrequests.create",
      "io.k8s.certificates.v1.certificatesigningrequests.approval.update"
    )
    and client.user.email is not null
    and gcp.audit.resource_name is not null
    and not client.user.email in (
      "system:gcp-controller-manager",
      "system:kube-controller-manager",
      "system:serviceaccount:kube-system:certificate-controller",
      "kubelet-bootstrap",
      "kubelet-nodepool-bootstrap"
    )
    and not client.user.email like "system:node:*"
| eval Esql.csr_name = replace(gcp.audit.resource_name, "/approval", "")
| stats
    Esql.create_count = count(*) where event.action == "io.k8s.certificates.v1.certificatesigningrequests.create",
    Esql.approval_count = count(*) where event.action == "io.k8s.certificates.v1.certificatesigningrequests.approval.update",
    Esql.event_action_values = values(event.action),
    Esql.timestamp_first_seen = min(@timestamp),
    Esql.timestamp_last_seen = max(@timestamp),
    Esql.source_ip_values = values(source.ip),
    Esql.user_agent_original_values = values(user_agent.original),
    Esql.data_stream_namespace_values = values(data_stream.namespace)
  by client.user.email, Esql.csr_name
| where Esql.create_count >= 1
    and Esql.approval_count >= 1
    and date_diff("seconds", Esql.timestamp_first_seen, Esql.timestamp_last_seen) <= 300
| keep client.user.email, Esql.*
'''

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1098"
name = "Account Manipulation"
reference = "https://attack.mitre.org/techniques/T1098/"

[[rule.threat.technique.subtechnique]]
id = "T1098.006"
name = "Additional Container Cluster Roles"
reference = "https://attack.mitre.org/techniques/T1098/006/"

[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1098"
name = "Account Manipulation"
reference = "https://attack.mitre.org/techniques/T1098/"

[[rule.threat.technique.subtechnique]]
id = "T1098.006"
name = "Additional Container Cluster Roles"
reference = "https://attack.mitre.org/techniques/T1098/006/"

[rule.threat.tactic]
id = "TA0004"
name = "Privilege Escalation"
reference = "https://attack.mitre.org/tactics/TA0004/"

[rule.investigation_fields]
field_names = [
    "client.user.email",
    "Esql.csr_name",
    "Esql.create_count",
    "Esql.approval_count",
    "Esql.event_action_values",
    "Esql.timestamp_first_seen",
    "Esql.timestamp_last_seen",
    "Esql.source_ip_values",
    "Esql.user_agent_original_values",
    "Esql.data_stream_namespace_values",
]