Multicast DNS implementations may respond to unicast queries that originate from sources outside of the local link network. Such responses may disclose information about network devices or be used in denial-of-service (DoS) amplification attacks.
Multicast DNS (mDNS) is a way for devices on a local link network to automatically discover other services and devices. In some implementations of mDNS, the mDNS server replies to unicast queries from outside the link local network (e.g., the WAN). This mDNS response may result in information disclosure of devices on the network. Furthermore, the information returned in the response is greater in size than the query and may be used for denial-of-service (DoS) amplification.
RFC 6762 Section 5.5 states the following:
An mDNS response to a unicast query originating outside of the local link network may result in information disclosure, such as disclosing the device type/model that responds to the request or the operating system running such software. The mDNS response may also be used to amplify denial of service attacks against other networks.
Block inbound and outbound mDNS on the WAN
Disable mDNS services
Despite attempts to analyze scan results, it is not entirely clear exactly which software responds to mDNS queries. Vendors have been alerted, but currently only a small number of devices have been confirmed to respond to unicast queries from the WAN. In Linux, the Avahi software is also known to allow unicast queries.
Cisco Systems, Inc.
D-Link Systems, Inc.
F5 Networks, Inc.
Ricoh Company Ltd.
Dell Computer Corporation, Inc.
Red Hat, Inc.
Thanks to Chad Seaman for reporting this vulnerability and assisting in coordination with vendors.
This document was written by Garret Wassermann.
|Date First Published:||2015-03-31|
|Date Last Updated:||2015-05-15 19:59 UTC|