SSD Advisory – Dasan Unauthenticated Remote Code Execution

Credit to Author: SSD / Maor Schwartz| Date: Wed, 06 Dec 2017 06:42:29 +0000

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Vulnerability Summary
The following advisory describes a buffer overflow that leads to remote code execution found in Dasan Networks GPON ONT WiFi Router H640X versions 12.02-01121 / 2.77p1-1124 / 3.03p2-1146

Dasan Networks GPON ONT WiFi Router “is indoor type ONT dedicated for FTTH (Fibre to the Home) or FTTP (Fiber to the Premises) deployments. That can work as simple Bridge or behave as Router/NAT. It’s cost-effective CPE that meets carrier-class requirement for Telcom industry and guarantee reliable service proven in the field.”

An independent security researcher, TigerPuma (at), has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program

Vendor response
We tried to contact Dasan since October 8 2017, repeated attempts to establish contact went unanswered. At this time there is no solution or workaround for this vulnerability.

Vulnerability details
All cgi in Dasan web service are symbolic link of cgipage.cgi, and when client request, lighttpd will invoke the corresponding path.

The buffer overflow vulnerability found in function login_action which handler login request.

The function uses strcpy without check length of input from client request.

If we will look at the stack, we can see that we can trigger the buffer overflow and in the end to control the pc.

Proof of Concept

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