Software Engineering Institute

Microsoft Windows systems use a caching domain name resolver service running on the computer to handle domain name service (DNS) requests and responses for applications. For example, when a user browses to www.microsoft.com in Internet Explorer, a DNS request is sent to some predetermined nameserver for an answer to the question, "What IP address should I connect to when looking for the machine that goes by the name 'www.microsoft.com'?" The answer returned (typically from the nameserver) is then stored in a cache which can then be reused when future requests for the same name information are made by other applications.

However, the Microsoft Windows domain name resolver service accepts responses from non-queried DNS servers by default. These resolvers will only match the source IP address of incoming response messages with their corresponding outgoing request destination IP addresses when the registry key named QueryIpMatching is set to "1". This essentially automatically fulfills one precondition necessary to trick victim DNS resolver clients into accepting attacker-determined domain name information.

When a remote attacker attempts to poison a victim resolver cache, QueryIpMatching may offer some benefit. Two pieces of information are then needed to perpetrate a domain name spoof attack (or directed service cache poisoning):

1. The address of the name server the victim expects responses from;
   
2. The query id expected in response to an outstanding name request made for an address the attacker is hoping to redirect.

Attackers able to successfully predict the query id of DNS requests initiated by client systems would be able to corrupt DNS responses and potentially misdirect network traffic and mislead victims. This could result in identity masquerading, loss of confidential information, denial of service, and other impacts typically associated with DNS cache corruption (cache pollution) or domain name information spoofing.

The previously-published solution utilizing the registry key IpQueryMatching does not work for all versions of Windows. Microsoft is currently investigating this issue and expects to provide more complete solution information in the near future.

Use cryptographic protection of either the site DNS or network traffic (i.e., use DNSSEC or IPSEC). Note use of DNSSEC may not be feasible by sites with older resolvers unable to validate DNSSEC-secured domain name information.