Bastille Tracking Number 19
CVE-2017-9477

Overview

A vulnerability has been discovered that enables an attacker to discover the CM MAC of a Comcast customer's gateway by connecting to the "xfinitywifi" hotspot running on the gateway. 



Affected Platforms

Cisco DPC3939, firmware version dpc3939-P20-18-v303r20421733-160420a-CMCST
Cisco DPC3939, firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST



Proof-of-Concept

When a user connects to an "xfinitywifi" hotspot on an affected gateway, the CM MAC, which is not normally known, is included in the DHCP ACK.



Test Environment

Cisco DPC3939, firmware version dpc3939-P20-18-v303r20421733-160420a-CMCST
Cisco DPC3939, firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST



Mitigation

Comcast customers can prevent this information leakage by disabling the "xfinitywifi" hotspot on their gateway.



Recommended Remediation

Configure the "xfinitywifi" DHCP server so that it does not leak the CM MAC.



Credits

Marc Newlin and Logan Lamb, Bastille
Chris Grayson, Web Sight.IO