Kubernetes Client Certificate Credential Created

Severity: informational
Group by: name, username
Compliance: Stratus Red Team k8s.persistence.create-client-certificate
Log types: Amazon.EKS.Audit, Azure.MonitorActivity, GCP.AuditLog
Tags: Kubernetes, Persistence, Credential Access, Unified Detection
Reference: https://stratus-red-team.cloud/attack-techniques/kubernetes/k8s.persistence.create-client-certificate/
Source: github.com/panther-labs/panther-analysis

Detects the creation of client certificate signing requests (CSRs) for Kubernetes API authentication. Attackers with appropriate RBAC permissions can create and approve client certificates to establish persistent access to the cluster. Client certificates provide long-term authentication that bypasses service account token expiration and can be harder to revoke. This technique is documented by Stratus Red Team as a persistence mechanism.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation
Credential Access	`T1552` Unsecured Credentials

Rule body yaml

AnalysisType: rule
RuleID: "Kubernetes.ClientCertificate.Created"
DisplayName: "Kubernetes Client Certificate Credential Created"
Enabled: true
Filename: k8s_client_certificate_created.py
LogTypes:
  - Amazon.EKS.Audit
  - Azure.MonitorActivity
  - GCP.AuditLog
Tags:
  - Kubernetes
  - Persistence
  - Credential Access
  - Unified Detection
Severity: Info
Description: >
  Detects the creation of client certificate signing requests (CSRs) for Kubernetes API authentication. Attackers with
  appropriate RBAC permissions can create and approve client certificates to establish persistent access to the cluster.
  Client certificates provide long-term authentication that bypasses service account token expiration and can be harder
  to revoke. This technique is documented by Stratus Red Team as a persistence mechanism.
Runbook: |
  1. Immediately investigate the user creating the certificate and verify if they are authorized to create client auth credentials
  2. Check if the CSR was approved and review who approved it within the last 10 minutes by searching audit logs for certificate approval events
  3. Search for API activity using the newly created certificate in the past 24 hours to identify any unauthorized access
Reports:
  Stratus Red Team:
    - k8s.persistence.create-client-certificate
  MITRE ATT&CK:
    - TA0003:T1098 # Persistence: Account Manipulation
    - TA0006:T1552 # Credential Access: Unsecured Credentials
Reference: https://stratus-red-team.cloud/attack-techniques/kubernetes/k8s.persistence.create-client-certificate/
DedupPeriodMinutes: 60
SummaryAttributes:
  - username
  - name
  - p_source_label
Tests:
  - Name: EKS client certificate CSR created
    ExpectedResult: true
    Log:
      {
        "kind": "Event",
        "apiVersion": "audit.k8s.io/v1",
        "verb": "create",
        "user": {"username": "attacker@example.com"},
        "sourceIPs": ["203.0.113.42"],
        "userAgent": "kubectl/v1.28.0",
        "objectRef": {
          "resource": "certificatesigningrequests",
          "name": "malicious-csr",
          "apiVersion": "certificates.k8s.io/v1"
        },
        "responseStatus": {"code": 201},
        "requestObject": {
          "apiVersion": "certificates.k8s.io/v1",
          "kind": "CertificateSigningRequest",
          "metadata": {"name": "malicious-csr"},
          "spec": {
            "groups": ["system:authenticated"],
            "request": "LS0tLS1CRUdJTiBDRVJUSUZJQ0FURSBSRVFVRVNULS0tLS0=",
            "signerName": "kubernetes.io/kube-apiserver-client",
            "usages": ["client auth"]
          }
        },
        "p_log_type": "Amazon.EKS.Audit",
        "p_source_label": "eks-cluster"
      }
  - Name: AKS client certificate CSR created
    ExpectedResult: true
    Log:
      {
        "p_log_type": "Azure.MonitorActivity",
        "category": "kube-audit",
        "operationName": "Microsoft.ContainerService/managedClusters/diagnosticLogs/Read",
        "properties": {
          "log": "{\"kind\":\"Event\",\"apiVersion\":\"audit.k8s.io/v1\",\"verb\":\"create\",\"user\":{\"username\":\"persistence-user@example.com\"},\"sourceIPs\":[\"1.2.3.4\"],\"objectRef\":{\"resource\":\"certificatesigningrequests\",\"name\":\"backdoor-cert\",\"apiVersion\":\"certificates.k8s.io/v1\"},\"responseStatus\":{\"code\":201},\"requestObject\":{\"spec\":{\"signerName\":\"kubernetes.io/kube-apiserver-client\",\"usages\":[\"client auth\"]}}}"
        },
        "p_source_label": "aks-cluster"
      }
  - Name: GKE client certificate CSR created
    ExpectedResult: true
    Log:
      {
        "protoPayload": {
          "authenticationInfo": {"principalEmail": "user@company.com"},
          "authorizationInfo": [{
            "granted": true,
            "permission": "io.k8s.certificates.v1.certificatesigningrequests.create",
            "resource": "certificates.k8s.io/v1/certificatesigningrequests/persistence-csr"
          }],
          "methodName": "io.k8s.certificates.v1.certificatesigningrequests.create",
          "requestMetadata": {"callerIP": "8.8.8.8"},
          "resourceName": "certificates.k8s.io/v1/certificatesigningrequests/persistence-csr",
          "serviceName": "k8s.io",
          "request": {
            "spec": {
              "signerName": "kubernetes.io/kube-apiserver-client",
              "usages": ["client auth"],
              "groups": ["system:authenticated"]
            }
          }
        },
        "resource": {
          "type": "k8s_cluster",
          "labels": {"project_id": "test-project"}
        },
        "p_log_type": "GCP.AuditLog",
        "p_source_label": "gke-cluster"
      }
  - Name: Service account creating certificate (higher severity)
    ExpectedResult: true
    Log:
      {
        "kind": "Event",
        "verb": "create",
        "user": {"username": "system:serviceaccount:default:compromised-sa"},
        "objectRef": {
          "resource": "certificatesigningrequests",
          "name": "sa-cert"
        },
        "responseStatus": {"code": 201},
        "requestObject": {
          "spec": {
            "signerName": "kubernetes.io/kube-apiserver-client",
            "usages": ["client auth"]
          }
        },
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: System principal creating certificate (excluded)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "create",
        "user": {"username": "system:kube-controller-manager"},
        "objectRef": {
          "resource": "certificatesigningrequests",
          "name": "system-cert"
        },
        "responseStatus": {"code": 201},
        "requestObject": {
          "spec": {
            "signerName": "kubernetes.io/kube-apiserver-client",
            "usages": ["client auth"]
          }
        },
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: AKS node bootstrap CSR (excluded)
    ExpectedResult: false
    Log:
      {
        "p_log_type": "Azure.MonitorActivity",
        "category": "kube-audit",
        "operationName": "Microsoft.ContainerService/managedClusters/diagnosticLogs/Read",
        "properties": {
          "log": "{\"kind\":\"Event\",\"apiVersion\":\"audit.k8s.io/v1\",\"verb\":\"create\",\"user\":{\"username\":\"kubelet-nodepool-bootstrap\"},\"sourceIPs\":[\"10.0.1.5\"],\"objectRef\":{\"resource\":\"certificatesigningrequests\",\"name\":\"node-csr-abc123\",\"apiVersion\":\"certificates.k8s.io/v1\"},\"responseStatus\":{\"code\":201},\"requestObject\":{\"spec\":{\"signerName\":\"kubernetes.io/kube-apiserver-client-kubelet\",\"usages\":[\"client auth\"]}}}"
        },
        "p_source_label": "aks-cluster"
      }
  - Name: Failed CSR creation (excluded)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "create",
        "user": {"username": "attacker@example.com"},
        "objectRef": {
          "resource": "certificatesigningrequests",
          "name": "failed-csr"
        },
        "responseStatus": {"code": 403},
        "requestObject": {
          "spec": {
            "signerName": "kubernetes.io/kube-apiserver-client",
            "usages": ["client auth"]
          }
        },
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: Server auth certificate (not client auth)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "create",
        "user": {"username": "admin@example.com"},
        "objectRef": {
          "resource": "certificatesigningrequests",
          "name": "server-cert"
        },
        "responseStatus": {"code": 201},
        "requestObject": {
          "spec": {
            "signerName": "kubernetes.io/kubelet-serving",
            "usages": ["server auth"]
          }
        },
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: Get CSR (not creation)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "get",
        "user": {"username": "admin@example.com"},
        "objectRef": {
          "resource": "certificatesigningrequests",
          "name": "existing-csr"
        },
        "responseStatus": {"code": 200},
        "p_log_type": "Amazon.EKS.Audit"
      }

Detection logic

Condition

not (verb ne "create" or resource ne "certificatesigningrequests")
not (responseStatus is_not_null and (responseStatus.code ge "400" or (responseStatus.code ge "1" and responseStatus.code le "16")))
not (username is_not_null and (username in ["masterclient", "aksService"] or (username starts_with "system:" and username not contains "serviceaccount")))
username ne "kubelet-nodepool-bootstrap"
requestObject.spec.usages contains "client auth" or requestObject.spec.signerName contains "kubernetes.io/kube-apiserver-client"

This rule also runs imperative logic the parser cannot express as a filter; the conditions above are the structured part it could extract.

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`username`	contains	`serviceaccount`
`username`	starts_with	`system:`
`username`	in	`aksService`, `masterclient`
`username`	is_not_null	(no value, null check)
`responseStatus.code`	ge	`1`
`responseStatus.code`	le	`16`
`responseStatus.code`	ge	`400`
`responseStatus`	is_not_null	(no value, null check)
`resource`	ne	`certificatesigningrequests`
`verb`	ne	`create`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`requestObject.spec.signerName`	contains	`kubernetes.io/kube-apiserver-client`
`requestObject.spec.usages`	contains	`client auth`
`username`	contains	`serviceaccount`
`username`	ne	`kubelet-nodepool-bootstrap`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`username`
`sourceIPs`
`userAgent`
`namespace`
`verb`
`resource`
`requestURI`
`responseStatus`
`cluster`	`p_source_label`
`name`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)