Pierluigi Paganini May 26, 2016

Leaked WPAD queries could result in domain name collisions with internal network naming schemes exposing corporate to MITM attacks.

The U.S. Computer Emergency Readiness Team(US-CERT) issued the Alert (TA16-144A) to warn of leaked WPAD queries could result in domain name collisions with internal network naming schemes. The WPAD queries are intended for resolution on private or enterprise DNS servers

A “domain name collision” bug could result in certain DNS queries to be resolved on public instead of private or enterprise servers, exposing organizations to Man-in-the-Middle (MitM) attacks.

Security experts explained observed Web Proxy Auto-Discovery (WPAD) Domain Name System (DNS) queries have been observed reaching public DNS.

The collisions could be abused by threat actors to configure an external proxy for network traffic, opening the door to man-in-the-middle (MitM) attacks.

The attack scenario is simple, it is enough that an attacker registers a domain to answer leaked WPAD queries and configures a valid proxy. The Domain name collision bug is particularly dangerous for private organizations, their assets (i.e. laptop) become vulnerable when used outside an internal network (e.g. home networks, public Wi-Fi networks).

The problem is even more serious is serious if we consider DNS queries using the Web Proxy Auto-Discovery protocol (WPAD) in combination with newer, publicly registered generic top-level domains, that could trigger resolution through queries erroneously passed to a public server.

Employees are particularly exposed when connecting a work computer to a home or external network, in this case, WPAD DNS queries may be made in error to public DNS servers.

“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.” states the Alert issued by the US CERT. “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.”

According to US-CERT, the WPAD is enabled by default in Windows and on Internet Explorer, and it is supported by the other OSs and browsers.

Below the list of recommendations issued by the US-CERT:

• 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 visitinghttps://forms.icann.org/en/help/name-collision/report-problems.

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Thank you

Pierluigi

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Pierluigi Paganini

(Security Affairs – WPAD , MITM)