TA16-144A: WPAD Name Collision Vulnerability

["US-CERT" <US-CERT () ncas us-cert gov>]

U.S. Department of Homeland Security US-CERT

National Cyber Awareness System:

 

TA16-144A: WPAD Name Collision Vulnerability [ https://www.us-cert.gov/ncas/alerts/TA16-144A ] 05/23/2016 07:38 AM EDT 
Original release date: May 23, 2016 | Last revised: June 01, 2016

Systems Affected

  * Windows, OS X, Linux systems, and web browsers with WPAD enabled 
  * Networks using unregistered or unreserved TLDs 

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 [ http://www.Verisign.com/CERTAlert ]]. 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 
[ https://www.icann.org/resources/pages/name-collision-2013-12-06-en ]] [3 [ 
https://newgtlds.icann.org/en/about/program ]]. Opportunistic domain registrants could abuse these collisions by 
configuring external proxies for network traffic and enabling man-in-the-middle (MitM) attacks across the Internet.

Description

WPAD is a protocol used to ensure all systems in an organization use 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 OS X 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 [ https://newgtlds.icann.org/en/about/program ]]. 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.

Other services (e.g., mail and internal web sites) may also perform DNS queries and attempt to automatically connect to 
supposedly internal DNS names [4 [ https://www.us-cert.gov/ncas/alerts/TA15-240A ]].

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).

The impact of other types of leaked DNS queries and connection attempts varies depending on the type of service and its 
configuration.

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 unless those systems 
will only be used on internal networks. 
  * Consider using a registered and fully qualified domain name (FQDN) from global DNS as the root for enterprise and 
other internal namespace. 
  * Consider using an internal TLD that is under your control and restricted from registration with the new gTLD 
program. Note that there is no assurance that the current list of “Reserved Names” from the new gTLD Applicant 
Guidebook (AGB) will remain reserved with subsequent rounds of new gTLDs [5 [ 
https://newgtlds.icann.org/en/applicants/agb/guidebook-full-04jun12-en.pdf ]]. 
  * 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 demonstrable severe harm due to name collision by visiting 
https://forms.icann.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 [ 
http://www.Verisign.com/CERTAlert ] 
  * [2] ICANN – Name Collision Resources & Information [ 
https://www.icann.org/resources/pages/name-collision-2013-12-06-en ] 
  * [3] ICANN – New gTLDs  [ https://newgtlds.icann.org/en/about/program ] 
  * [4] US-CERT – Controlling Outbound DNS Access  [ https://www.us-cert.gov/ncas/alerts/TA15-240A ] 
  * [5] ICANN – gTLD Applicant Guidebook [ https://newgtlds.icann.org/en/applicants/agb/guidebook-full-04jun12-en.pdf ] 

Revision History

  * May 23, 2016: Initial Release 
  * June 1, 2016: Added information on using TLDs restricted from registration with the gTLD program 
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