Rewterz Threat Advisory – Exploitation of automatic DNS registration and auto-discovery

DNS auto-registration and auto-discovery can be used as proxy for gathering network packets, violating confidentiality.

IMPACT:  NORMAL

PUBLISH DATE:  06-09-2018

OVERVIEW

If a malicious device is added to a network with the name ‘WPAD’ by a user with network access, they may use DNS auto-registration and auto-discovery to work as a proxy for victims on the network. This leads to a loss of confidentiality and integrity of any activity on the network.

ANALYSIS

Routers auto-registering names on LANs may lead to a breach in confidentiality and integrity of any network activity by exposing network packets. Many customer-premise routers have a convenience feature to support LAN based device discovery. They register by default a DNS A-record based on the names of device that visit LAN. Name for the A record is taken from the name supplied in the DHCP request of the visiting device.

This can be exploited with Proxy Auto-Configuration, based on the WPAD method. Other auto-discovery names like ISATAP, autodiscovery and autoconf may also serve for attack vectors.

Researchers reproduced PAC discovery based on WPAD name propagated through mDNS without cooperation of the LAN/WLAN router.

It has also been discovered that the protections against rogue DHCP servers or router advisements do not work against this sort of attack.

AFFECTED PRODUCTS

MITIGATION

For a short-term solution, home/office LAN/WLAN routers should not auto-register to their local DNS magic names related to autoconfiguration. Furthermore, mDNS based names should not be accepted by auto-discovery features as authoritative sources.