Kubernetes CronJob Created or Modified

Status: Experimental
Severity: informational
Group by: namespace, username
Log types: Amazon.EKS.Audit, Azure.MonitorActivity, GCP.AuditLog
Tags: Kubernetes, Security Control, Persistence, Scheduled Task, Unified Detection
Reference: https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/
Source: github.com/panther-labs/panther-analysis

This detection monitors for creation or modification of CronJobs in Kubernetes clusters. Attackers may create or modify scheduled jobs to achieve cluster persistence, execute malicious code on a schedule, or maintain backdoor access to compromised clusters. This detection works across AWS EKS, Azure AKS, and GCP GKE clusters.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1053.003` Scheduled Task/Job: Cron

Rule body yaml

AnalysisType: rule
RuleID: "Kubernetes.CronJob.CreatedOrModified"
DisplayName: "Kubernetes CronJob Created or Modified"
Enabled: true
Status: Experimental
Filename: k8s_cronjob_created_or_modified.py
LogTypes:
  - Amazon.EKS.Audit
  - Azure.MonitorActivity
  - GCP.AuditLog
Tags:
  - Kubernetes
  - Security Control
  - Persistence
  - Scheduled Task
  - Unified Detection
Severity: Info
Description: >
  This detection monitors for creation or modification of CronJobs in Kubernetes clusters.
  Attackers may create or modify scheduled jobs to achieve cluster persistence, execute
  malicious code on a schedule, or maintain backdoor access to compromised clusters.
  This detection works across AWS EKS, Azure AKS, and GCP GKE clusters.
Runbook: |
  1. Query all CronJob creation and modification events by username in the 24 hours before the alert to establish deployment patterns
  2. Analyze the CronJob schedule specification and container image from requestObject to identify suspicious commands or known malicious patterns
  3. Search for other CronJobs created by this user in the past 30 days to determine if this represents established activity or anomalous behavior
Reference: https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/
Reports:
  MITRE ATT&CK:
    - TA0003:T1053.003 # Persistence: Scheduled Task/Job - Cron
DedupPeriodMinutes: 60
SummaryAttributes:
  - username
  - namespace
  - p_source_label
Tests:
  - Name: EKS CronJob Created
    ExpectedResult: true
    Log:
      {
        "kind": "Event",
        "apiVersion": "audit.k8s.io/v1",
        "auditID": "abc-123",
        "verb": "create",
        "user": {"username": "admin@example.com"},
        "sourceIPs": ["1.2.3.4"],
        "userAgent": "kubectl/v1.28.0",
        "objectRef": {
          "resource": "cronjobs",
          "namespace": "default",
          "name": "backup-job",
          "apiVersion": "batch/v1"
        },
        "responseStatus": {"code": 201},
        "requestURI": "/apis/batch/v1/namespaces/default/cronjobs",
        "requestObject": {
          "kind": "CronJob",
          "metadata": {"name": "backup-job", "namespace": "default"},
          "spec": {
            "schedule": "0 2 * * *",
            "jobTemplate": {
              "spec": {
                "template": {
                  "spec": {
                    "containers": [{
                      "name": "backup",
                      "image": "backup:latest"
                    }]
                  }
                }
              }
            }
          }
        },
        "p_log_type": "Amazon.EKS.Audit",
        "p_source_label": "eks-cluster"
      }
  - Name: AKS CronJob Updated
    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\":\"update\",\"user\":{\"username\":\"admin@example.com\"},\"sourceIPs\":[\"10.0.0.1\"],\"objectRef\":{\"resource\":\"cronjobs\",\"namespace\":\"production\",\"name\":\"nightly-job\"},\"responseStatus\":{\"code\":200},\"requestURI\":\"/apis/batch/v1/namespaces/production/cronjobs/nightly-job\"}"
        },
        "p_source_label": "aks-cluster"
      }
  - Name: GCP GKE CronJob Created
    ExpectedResult: true
    Log:
      {
        "protoPayload": {
          "authenticationInfo": {"principalEmail": "user@company.com"},
          "authorizationInfo": [{
            "granted": true,
            "permission": "io.k8s.batch.v1.cronjobs.create",
            "resource": "batch/v1/namespaces/default/cronjobs/backup-job"
          }],
          "methodName": "io.k8s.batch.v1.cronjobs.create",
          "requestMetadata": {
            "callerIP": "1.2.3.4",
            "callerSuppliedUserAgent": "kubectl/v1.27.0"
          },
          "resourceName": "batch/v1/namespaces/default/cronjobs/backup-job",
          "serviceName": "k8s.io",
          "request": {
            "kind": "CronJob",
            "metadata": {"name": "backup-job"},
            "spec": {"schedule": "0 2 * * *"}
          }
        },
        "resource": {
          "type": "k8s_cluster",
          "labels": {"project_id": "test-project"}
        },
        "p_log_type": "GCP.AuditLog",
        "p_source_label": "gke-cluster"
      }
  - Name: CronJob Creation Failed
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "create",
        "objectRef": {
          "resource": "cronjobs",
          "namespace": "default",
          "name": "test-job"
        },
        "responseStatus": {"code": 403, "status": "Failure"},
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: Pod Creation (Not CronJob)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "create",
        "objectRef": {
          "resource": "pods",
          "namespace": "default"
        },
        "responseStatus": {"code": 201},
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: CronJob Get (Not Create/Update)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "verb": "get",
        "objectRef": {
          "resource": "cronjobs",
          "namespace": "default",
          "name": "existing-job"
        },
        "responseStatus": {"code": 200},
        "p_log_type": "Amazon.EKS.Audit"
      }
  - Name: System controller creating CronJob in kube-system (excluded)
    ExpectedResult: false
    Log:
      {
        "kind": "Event",
        "apiVersion": "audit.k8s.io/v1",
        "verb": "create",
        "user": {"username": "system:serviceaccount:kube-system:cronjob-controller"},
        "sourceIPs": ["10.0.0.1"],
        "objectRef": {
          "resource": "cronjobs",
          "namespace": "kube-system",
          "name": "system-cleanup",
          "apiVersion": "batch/v1"
        },
        "responseStatus": {"code": 201},
        "p_log_type": "Amazon.EKS.Audit",
        "p_source_label": "eks-cluster"
      }

Detection logic

Condition

verb in ["create", "update", "patch"]
resource eq "cronjobs"
not (responseStatus is_not_null and (responseStatus.code ge "400" or (responseStatus.code ge "1" and responseStatus.code le "16")))
subresource ne "status"
not (namespace is_not_null and namespace in ["kube-system", "gke-system", "kube-node-lease", "kube-public"] and username is_not_null and (username in ["masterclient", "aksService"] or (username starts_with "system:" and username not contains "serviceaccount")))

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`
`namespace`	in	`gke-system`, `kube-node-lease`, `kube-public`, `kube-system`
`namespace`	is_not_null	(no value, null check)
`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)

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
`resource`	eq	`cronjobs`
`subresource`	ne	`status`
`username`	contains	`serviceaccount`
`verb`	in	`create` `patch` `update`

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)