CVE-2021-3493 Comprehensive Exploit Framework ${\color{#FF4D2E} \textbf{\textsf{[DeepRoot]}}}$

OverlayFS Capability Privilege Escalation Framework - Red Team Professional Edition

Overview

DeepRoot framework is a comprehensive privilege escalation exploit for CVE-2021-3493 (OverlayFS Privilege Escalation) with advanced red team features including persistence mechanisms, stealth capabilities, and post-exploitation modules.

Created by: George S. Yanni
Original Advisory: https://ssd-disclosure.com/ssd-advisory-overlayfs-pe/

---

⚠️ WARNING

FOR EDUCATIONAL AND AUTHORIZED TESTING PURPOSES ONLY

DeepRoot framework is designed for:

• Security research and education
• Authorized penetration testing
• Red team exercises with explicit permission
• Vulnerability assessment in controlled environments

DO NOT use against production systems without explicit authorization. Unauthorized access to computer systems is illegal.

---

Vulnerability Details

CVE-2021-3493 is a privilege escalation vulnerability in the Linux OverlayFS filesystem that allows an unprivileged user to gain root privileges by exploiting improper capability handling in user namespaces.

Key Characteristics:

• Exploits OverlayFS capability handling bug
• Uses user namespaces (CLONE_NEWUSER) to map UID 0
• Uses mount namespaces (CLONE_NEWNS) for isolated mounts
• Sets file capabilities on binaries via setxattr()
• Works on systems with user namespaces enabled

---

Features

Core Exploit

• Privilege Escalation: Reliable root access via OverlayFS vulnerability
• Namespace Isolation: Uses user and mount namespaces for safe exploitation
• Capability Injection: Sets CAP_ALL_EP (all capabilities) on target binary
• Stealth Mode: Optional stealth features to reduce detection

Persistence Mechanisms

1. SSH Backdoor - Inject SSH public key for root access
2. Sudo Backdoor - Modify sudoers to allow passwordless root access
3. Cron Persistence - Install cron jobs for recurring execution
4. Systemd Service - Create systemd service for boot persistence
5. LD_PRELOAD Backdoor - Hook library functions for code injection

Post-Exploitation

6. System Information Collection - Gather system reconnaissance data
7. Credential Search - Find passwords, keys, and sensitive files
8. Lateral Movement - Identify SSH keys and network opportunities
9. C2 Connection Testing - Verify network connectivity for C2 setup

Utilities

• Shell Access - Direct root shell spawn
• Cleanup - Remove exploit artifacts

---

File Structure

CVE-2021-3493/
├── comprehensive.c          # Main exploit source code
├── README.md                # This file
│
├── Option_1_Inject_SSH_backdoor_key/
│   └── README.md            # SSH backdoor guide
│
├── Option_2_Install_sudo_backdoor/
│   └── README.md            # Sudo backdoor guide
│
├── Option_3_Install_cron_persistence/
│   └── README.md            # Cron persistence guide
│
├── Option_4_Install_systemd_service/
│   └── README.md            # Systemd service guide
│
├── Option_5_Install_LD_PRELOAD_backdoor/
│   └── README.md            # LD_PRELOAD backdoor guide
│
├── Option_6_Collect_system_information/
│   └── README.md            # System info collection guide
│
├── Option_7_Search_for_credentials/
│   └── README.md            # Credential search guide
│
├── Option_8_Check_lateral_movement/
│   └── README.md            # Lateral movement guide
│
├── Option_9_Establish_C2_connection/
│   └── README.md            # C2 connection guide
│
├── Option_Shell_and_Cleanup/
│   └── README.md            # Shell and cleanup guide
│
└── Stealth_Mode_Guide/
    └── README.md            # Stealth mode documentation

---

Quick Start

Compilation

gcc -o comprehensive comprehensive.c

Basic Usage

# Run the exploit
./comprehensive

# The exploit will:
# 1. Create necessary directories (./ovlcap/)
# 2. Set up user and mount namespaces
# 3. Mount OverlayFS
# 4. Set capabilities on binary
# 5. Execute privileged binary
# 6. Present post-exploitation menu

Post-Exploitation Menu

After successful privilege escalation, you'll see:

╔══════════════════════════════════════════════════╗
║        POST-EXPLOITATION MENU                    ║
╚══════════════════════════════════════════════════╝

Available actions:
  1. Inject SSH backdoor key
  2. Install sudo backdoor
  3. Install cron persistence
  4. Install systemd service
  5. Install LD_PRELOAD backdoor
  6. Collect system information
  7. Search for credentials
  8. Check lateral movement
  9. Establish C2 connection
  s. Spawn root shell
  0. Cleanup and exit

Select option:

---

Detailed Documentation

Each option has its own documentation folder with complete guides:

Persistence Options

• Option 1: SSH Backdoor - Inject SSH public key for persistent root access
• Option 2: Sudo Backdoor - Modify sudoers for passwordless root access
• Option 3: Cron Persistence - Install cron jobs for recurring execution
• Option 4: Systemd Service - Create systemd service for boot persistence
• Option 5: LD_PRELOAD Backdoor - Hook library functions to inject code

Post-Exploitation Options

• Option 6: System Information - Collect system reconnaissance data
• Option 7: Credential Search - Search for passwords and sensitive files
• Option 8: Lateral Movement - Find SSH keys and network opportunities
• Option 9: C2 Connection - Test network connectivity for C2 setup

Utilities

• Shell and Cleanup - Spawn root shell or cleanup artifacts
• Stealth Mode Guide - Documentation for stealth features

---

Requirements

System Requirements

• Linux system (kernel with OverlayFS support)
• User namespaces enabled (kernel.unprivileged_userns_clone=1 or CAP_SYS_ADMIN)
• GCC compiler
• Root access NOT required initially (that's the point!)

Kernel Compatibility

The exploit targets systems vulnerable to CVE-2021-3493. Check your kernel version and ensure user namespaces are available.

---

How It Works

Exploit Flow

1. Namespace Creation: Creates new user and mount namespaces using unshare(CLONE_NEWNS | CLONE_NEWUSER)

2. UID/GID Mapping: Maps current unprivileged UID to 0 (root) within the new namespace via /proc/self/uid_map and /proc/self/gid_map

3. OverlayFS Mount: Mounts OverlayFS with lower, upper, and work directories

4. Binary Copy: Copies the exploit binary to the overlay merge directory

5. Capability Injection: Uses setxattr() to set CAP_ALL_EP (all capabilities, effective and permitted) on the copied binary

6. Privileged Execution: Executes the binary from the upper directory, which has full capabilities and runs as root

Technical Details

• User Namespace: Allows mapping of UIDs/GIDs within isolated namespace
• Mount Namespace: Creates isolated mount point for OverlayFS
• File Capabilities: Linux capability system allows fine-grained privileges on files
• OverlayFS: Merges multiple directory trees, upper directory takes precedence

---

Stealth Features

The exploit includes optional stealth mode (--stealth flag) that:

• Reduces logging verbosity
• Lowers process priority (nice(19))
• Prevents core dumps
• Clears environment variables
• Modifies file timestamps

See Stealth Mode Guide for details.

---

Examples

Basic Privilege Escalation

./comprehensive
# Wait for menu, select 's' for shell

Install SSH Backdoor

./comprehensive
# Select option 1
# Follow prompts to inject your SSH public key

Install Cron Persistence

./comprehensive
# Select option 3
# Cron job installed, runs every 5 minutes

Stealth Mode

./comprehensive --stealth
# Exploit runs with reduced logging and OPSEC features

Legal and Ethical Considerations

IMPORTANT DISCLAIMERS:

1. Authorization Required: Only use DeepRoot on systems you own or have explicit written permission to test

2. Legal Liability: Unauthorized access to computer systems is illegal in most jurisdictions. You are solely responsible for your actions

3. Educational Purpose: DeepRoot is provided for educational and research purposes

4. No Warranty: This software is provided "as is" without warranty of any kind

5. Ethical Use: Use responsibly and ethically. Do not harm systems or data

---

Credits

• DeepRoot Development: George S. Yanni
• Vulnerability: CVE-2021-3493 (OverlayFS Privilege Escalation)
• Original Advisory: SSD Advisory - OverlayFS PE

---

License

DeepRoot is provided for educational purposes. Use at your own risk.

---

Contributing

This is an educational project. Contributions, bug reports, and improvements are welcome, but please ensure all code maintains the educational and ethical standards of this project.

---

Remember: With great power comes great responsibility. Use DeepRoot ethically and legally.

${\color{3DA300}- \text{George S. Yanni}}$

Feedback & Contact

For any recommendations, improvements, bug reports, or questions about DeepRoot, feel free to reach out on LinkedIn .