U.S. Department of Homeland Security US-CERT

National Cyber Awareness System:



TA16-144A: WPAD Name Collision Vulnerability
05/23/2016 07:38 AM EDT


Original release date: May 23, 2016

Systems Affected
Windows, OS X, Linux systems, and web browsers with WPAD enabled

Overview
Web Proxy Auto-Discovery (WPAD) Domain Name System (DNS) queries that are
intended for resolution on private or enterprise DNS servers have been
observed reaching public DNS servers [1]. In combination with the New generic
Top Level Domain (gTLD) program’s incorporation of previously undelegated
gTLDs for public registration, leaked WPAD queries could result in domain name
collisions with internal network naming schemes [2] [3]. Collisions could be
abused by opportunistic domain registrants to configure an external proxy for
network traffic, allowing the potential for man-in-the-middle (MitM) attacks
across the Internet.

Description
WPAD is a protocol used to ensure all systems in an organization utilize the
same web proxy configuration. Instead of individually modifying configurations
on each device connected to a network, WPAD locates a proxy configuration file
and applies the configuration automatically.

The use of WPAD is enabled by default on all Microsoft Windows operating
systems and Internet Explorer browsers. WPAD is supported but not enabled by
default on Mac and Linux-based operating systems, as well as, Safari, Chrome,
and Firefox browsers.

With the New gTLD program, previously undelegated gTLD strings are now being
delegated for public domain name registration [3]. These strings may be used
by private or enterprise networks, and in certain circumstances, such as when
a work computer is connected from a home or external network, WPAD DNS queries
may be made in error to public DNS servers. Attackers may exploit such leaked
WPAD queries by registering the leaked domain and setting up MitM proxy
configuration files on the Internet.


Impact
Leaked WPAD queries could result in domain name collisions with internal
network naming schemes. If an attacker registers a domain to answer leaked
WPAD queries and configures a valid proxy, there is potential to conduct
man-in-the-middle (MitM) attacks across the Internet.

The WPAD vulnerability is significant to corporate assets such as laptops. In
some cases these assets are vulnerable even while at work but observations
indicate that most assets become vulnerable when used outside an internal
network (e.g. home networks, public Wi-Fi networks).

Solution
US-CERT encourages users and network administrators to implement the following
recommendations to provide a more secure and efficient network infrastructure:

Consider disabling automatic proxy discovery/configuration in browsers and
operating systems during device setup if it will not be used for internal
networks.
Consider using a fully qualified domain name (FQDN) from global DNS as the
root for enterprise and other internal namespace.
Configure internal DNS servers to respond authoritatively to internal TLD
queries.
Configure firewalls and proxies to log and block outbound requests for
wpad.dat files.
Identify expected WPAD network traffic and monitor the public namespace or
consider registering domains defensively to avoid future name collisions.
File a report with ICANN if your system is suffering demonstrably severe harm
as a consequence of name collision by visiting https://forms.ica
n.org/en/help/name-collision/report-problems.
References
[1] Verisign – MitM Attack by Name Collision: Cause Analysis and Vulnerability
Assessment in the New gTLD Era
[2] ICANN – Name Collision Resources & Information
[3] ICANN – New gTLDs
[4] US-CERT – Controlling Outbound DNS Access
Revision History
May 23, 2016: Initial Release

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