CIS 1.9 Kubernetes Policies Checks 5.1.5 returns an error when run inside a pod

[winkrs]

Overview

      - id: 5.1.5
        text: "Ensure that default service accounts are not actively used. (Automated)"
        audit: |
          kubectl get serviceaccount --all-namespaces --field-selector metadata.name=default -o=json | jq -r '.items[] | " namespace: \(.metadata.namespace), kind: \(.kind), name: \(.metadata.name), automountServiceAccountToken: \(.automountServiceAccountToken | if . == null then "notset" else . end )"' | xargs -L 1
        use_multiple_values: true
        tests:
          test_items:
            - flag: "automountServiceAccountToken"
              compare:
                op: eq
                value: false
              set: true
        remediation: |
          Create explicit service accounts wherever a Kubernetes workload requires specific access
          to the Kubernetes API server.
          Modify the configuration of each default service account to include this value
          `automountServiceAccountToken: false`.
        scored: true

The audit script failed to run as the version of xargs contain unrecognizing option L.

How did you run kube-bench?

I'm running kube-bench inside a pod using the job.yaml.

command used: kube-bench --json --check=5.1.5

What happened?

The audit script return error with the following reason:

failed to run: "kubectl get serviceaccount --all-namespaces --field-selector metadata.name=default -o=json | jq -r '.items[] | \" namespace: \\(.metadata.namespace), kind: \\(.kind), name: \\(.metadata.name), automountServiceAccountToken: \\(.automountServiceAccountToken | if . == null then \"notset\" else . end )\"' | xargs -L 1", output: "xargs: unrecognized option: L
BusyBox v1.36.1 (2024-06-10 07:11:47 UTC) multi-call binary.

Usage: xargs [OPTIONS] [PROG ARGS]

Run PROG on every item given by stdin

	-0	NUL terminated input
	-a FILE	Read from FILE instead of stdin
	-o	Reopen stdin as /dev/tty
	-r	Don't run command if input is empty
	-t	Print the command on stderr before execution
	-p	Ask user whether to run each command
	-E STR,-e[STR]	STR stops input processing
	-I STR	Replace STR within PROG ARGS with input line
	-n N	Pass no more than N args to PROG
	-s N	Pass command line of no more than N bytes
	-P N	Run up to N PROGs in parallel
	-x	Exit if size is exceeded
", error: exit status 1

Here is log from the pod in json format.

{
    "Controls": [
        {
            "id": "4",
            "version": "cis-1.9",
            "detected_version": "1.27",
            "text": "Worker Node Security Configuration",
            "node_type": "node",
            "tests": null,
            "total_pass": 0,
            "total_fail": 0,
            "total_warn": 0,
            "total_info": 0
        },
        {
            "id": "5",
            "version": "cis-1.9",
            "detected_version": "1.27",
            "text": "Kubernetes Policies",
            "node_type": "policies",
            "tests": [
                {
                    "section": "5.1",
                    "type": "",
                    "pass": 0,
                    "fail": 1,
                    "warn": 0,
                    "info": 0,
                    "desc": "RBAC and Service Accounts",
                    "results": [
                        {
                            "test_number": "5.1.5",
                            "test_desc": "Ensure that default service accounts are not actively used. (Automated)",
                            "audit": "kubectl get serviceaccount --all-namespaces --field-selector metadata.name=default -o=json | jq -r '.items[] | \" namespace: \\(.metadata.namespace), kind: \\(.kind), name: \\(.metadata.name), automountServiceAccountToken: \\(.automountServiceAccountToken | if . == null then \"notset\" else . end )\"' | xargs -L 1\n",
                            "AuditEnv": "",
                            "AuditConfig": "",
                            "type": "",
                            "remediation": "Create explicit service accounts wherever a Kubernetes workload requires specific access\nto the Kubernetes API server.\nModify the configuration of each default service account to include this value\n`automountServiceAccountToken: false`.\n",
                            "test_info": [
                                "Create explicit service accounts wherever a Kubernetes workload requires specific access\nto the Kubernetes API server.\nModify the configuration of each default service account to include this value\n`automountServiceAccountToken: false`.\n"
                            ],
                            "status": "FAIL",
                            "actual_value": "",
                            "scored": true,
                            "IsMultiple": true,
                            "expected_result": "",
                            "reason": "failed to run: \"kubectl get serviceaccount --all-namespaces --field-selector metadata.name=default -o=json | jq -r '.items[] | \\\" namespace: \\\\(.metadata.namespace), kind: \\\\(.kind), name: \\\\(.metadata.name), automountServiceAccountToken: \\\\(.automountServiceAccountToken | if . == null then \\\"notset\\\" else . end )\\\"' | xargs -L 1\", output: \"xargs: unrecognized option: L\nBusyBox v1.36.1 (2024-06-10 07:11:47 UTC) multi-call binary.\n\nUsage: xargs [OPTIONS] [PROG ARGS]\n\nRun PROG on every item given by stdin\n\n\t-0\tNUL terminated input\n\t-a FILE\tRead from FILE instead of stdin\n\t-o\tReopen stdin as /dev/tty\n\t-r\tDon't run command if input is empty\n\t-t\tPrint the command on stderr before execution\n\t-p\tAsk user whether to run each command\n\t-E STR,-e[STR]\tSTR stops input processing\n\t-I STR\tReplace STR within PROG ARGS with input line\n\t-n N\tPass no more than N args to PROG\n\t-s N\tPass command line of no more than N bytes\n\t-P N\tRun up to N PROGs in parallel\n\t-x\tExit if size is exceeded\n\", error: exit status 1"
                        }
                    ]
                }
            ],
            "total_pass": 0,
            "total_fail": 1,
            "total_warn": 0,
            "total_info": 0
        }
    ],
    "Totals": {
        "total_pass": 0,
        "total_fail": 1,
        "total_warn": 0,
        "total_info": 0
    }
}

What did you expect to happen:

The audit script to run successfully as it did when run outside the pod.

Environment

kube-bench version: v1.8.0
kubectl version: v1.27.15

Fix:

Need to update Dockerfile line 24 to add package findutils as shown below. This ensures that the GNU version of xargs is available inside the pod,

RUN apk --no-cache add procps findutils