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Docker Explorer

This project helps a forensics analyst explore offline Docker filesystems.

This is not an officially supported Google product.

If you're looking for similar capabilities on Containerd systems, feel free to check https://github.com/google/container-explorer.

Overview

When analyzing a system where a Docker container has been compromised, it can be useful to have the same view of the filesystem as the container's.

Docker uses layered backend filesystems like AuFS or OverlayFS.

Each layer is actually stored on the host's filesystem as multiple folders, and some JSON files are used by Docker to know what is what;

Installation

PPA

A .deb package is available in the GIFT PPA

add-apt-repository ppa:gift/stable
apt update
apt install docker-explorer-tools

PyPI

This project is released on PyPi.

virtualenv docker-explorer ; cd docker-explorer ; source bin/activate
pip install docker-explorer

Source

You can clone this repository, as running the script doesn't require any external dependency.

Usage

For the forensicator, this usually goes:

  1. find the interesting container ID
  2. mount the container's filesystem in /mnt/container
  3. log2timeline.py /tmp/container.plaso /mnt/container
  4. or ls -lta /mnt/container/tmp

List the running containers

On a live host running the compromised container you would run:

# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED         STATUS              PORTS               NAMES
7b02fb3e8a66        busybox             "sleep 10d"         19 hours ago    Up 19 hours                             dreamy_snyder

If you mount the disk image of the same host in /mnt/root, you can use de.py to access the same information:

# de.py -r /mnt/root/var/lib/docker list running_containers
[
    {
        "container_id": "7b02fb3e8a665a63e32b909af5babb7d6ba0b64e10003b2d9534c7d5f2af8966",
        "image_id": "7968321274dc6b6171697c33df7815310468e694ac5be0ec03ff053bb135e768",
        "image_name": "busybox",
        "start_date": "2016-09-16T11:50:15.253796"
    }
]

Mount the container's filesystem:

On a live host running the compromised container you would run:

# find ID of your running container:
docker ps

# create image (snapshot) from container filesystem
docker commit 12345678904b5 mysnapshot

# explore this filesystem using bash (for example)
docker run -t -i mysnapshot /bin/bash

If you mount the disk image of the same host in /mnt/root, you can use de.py to access the same information:

# de.py -r /tmp/ mount 7b02fb3e8a665a63e32b909af5babb7d6ba0b64e10003b2d9534c7d5f2af8966 /tmp
You'll needs the aufs-tools package. If you install aufs-tools, I can run these for you.

Whoops... Let's try again

# apt install aufs-tools
# de.py -r /tmp/ mount 7b02fb3e8a665a63e32b909af5babb7d6ba0b64e10003b2d9534c7d5f2af8966 /tmp/test
mount -t aufs -o ro,br=/tmp/docker/aufs/diff/b16a494082bba0091e572b58ff80af1b7b5d28737a3eedbe01e73cd7f4e01d23=ro+wh none /tmp/test
mount -t aufs -o ro,remount,append:/tmp/docker/aufs/diff/b16a494082bba0091e572b58ff80af1b7b5d28737a3eedbe01e73cd7f4e01d23-init=ro+wh none /tmp/test
mount -t aufs -o ro,remount,append:/tmp/docker/aufs/diff/d1c54c46d331de21587a16397e8bd95bdbb1015e1a04797c76de128107da83ae=ro+wh none /tmp/test
root@test-VirtualBox:~# ls /tmp/test
bin  dev  etc  home  proc  root  sys  tmp  usr  var

Show a container's image history

On the live host:

# docker history 7968321274dc6b6171697c33df7815310468e694ac5be0ec03ff053bb135e768
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
7968321274dc        4 weeks ago         /bin/sh -c #(nop)  CMD ["sh"]                   0 B
<missing>           4 weeks ago         /bin/sh -c #(nop) ADD file:707e63805c0be1a226   1.11 MB

On a disk image mounted in /mnt/root:

# de.py -r /mnt/root/var/lib/docker history 7b02fb3e8a665a63e32b909af5babb7d6ba0b64e10003b2d9534c7d5f2af8966
{
    "sha256:7968321274dc6b6171697c33df7815310468e694ac5be0ec03ff053bb135e768": {
        "container_cmd": "/bin/sh -c #(nop)  CMD [\"sh\"]",
        "created_at : "2018-09-20T18:41:05.770133",
        "size" : 0
    }
}

Troubleshooting

If on your Ubuntu system you get the errors:

mount: unknown filesystem type 'aufs'
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
/sbin/mount.aufs:proc_mnt.c:96: /mnt/aufs: Invalid argument
....

Try this:

sudo apt-get install linux-image-extra-$(uname -r)

Maintainer notes

Gift PPA push

Make sure the following is installed:

sudo apt install dh-python flex byacc quilt python3-all-dev libdistro-info-perl

For the GPG signing part, running over SSH with a gpg-agent running might confuse gpg and ask for the passphrase on the $DISPLAY. To prevent this, you can run gpgconf --kill gpg-agent.

Make a new version tag:

DATE="$(date +%Y%m%d)"
git checkout main
git pull upstream main
git tag "${DATE}"
git push upstream "${DATE}"

Build with l2tdevtools.

cd /tmp
git clone https://github.com/log2timeline/l2tdevtools

Make the build environment:

mkdir /tmp/build ; cd /tmp/build

First we need 2 files, post-dpkg-source.sh:

cat <<EOF >post-dpkg-source.sh
PROJECT=\$1;
VERSION=\$2;
VERSION_SUFFIX=\$3;
DISTRIBUTION=\$4;
ARCHITECTURE=\$5;

dput ppa:docker-explorer-dev-team_staging ../\${PROJECT}_\${VERSION}-1\${VERSION_SUFFIX}~\${DISTRIBUTION}_\${ARCHITECTURE}.changes
EOF

and prep-dpkg-source.sh:

cat <<EOF >prep-dpkg-source.sh
export NAME="Docker-Explorer devs";
export EMAIL="docker-explorer-devs@google.com";

PROJECT=\$1;
VERSION=\$2;
VERSION_SUFFIX=\$3;
DISTRIBUTION=\$4;
ARCHITECTURE=\$5;

dch --preserve -v \${VERSION}-1\${VERSION_SUFFIX}~\${DISTRIBUTION} --distribution \${DISTRIBUTION} --urgency low "Modifications for PPA release."
EOF

These are also stored in /tmp/build

Then go to https://github.com/google/docker-explorer/releases and create a new release.

Start the build:

PYTHONPATH=. python3 tools/build.py --build-directory=/tmp/build/  --project docker-explorer dpkg-source --distributions focal,jammy,noble

Then upload the packages to the PPA:

cd /tmp/build/
dput ppa:docker-explorer-devs_staging docker-explorer_<VERSION>_source.changes

Then wait for launchpad to build the package, and move it from ppa:docker-explorer-dev-team_staging to ppa:gift_stable, by going to https://launchpad.net/~docker-explorer-devs/+archive/ubuntu/staging/+copy-packages

Upload to PyPi

First make sure the proper version is set in docker-explorer/__init__.py.

Then run

sudo apt install twine
python3 setup.py sdist
python3 -m twine upload  dist/*