Dear all, We would like to invite you to a briefing session attended by Dave Piscitello from the Security and Stability Advisory Committee (SSAC) on DNS Response Modification. The briefing will be on Wednesday September 17th from 1300 to 1400 UTC and will be simultaneously interpreted into French and Spanish. Please find the SSAC Advisory on DNS Response Modification and participation instructions on the meeting page. You will shortly be able to find a link to follow the presentation using Adobe Connect on the same page. https://st.icann.org/alac/index.cgi?dns_response_modification What is DNS Response Modification? In their preliminary report number 32, the SSAC describes the practise of DNS response modification by entrusted agents or third parties. In the first case, an entrusted agent receives a DNS query for a name. The entrusted agent determines that the name in the query does not exist in the zone file it hosts for the domain registrant but rather than returning a DNS response indicating a non-existent name, the entrusted agent returns a response indicating the name exists and containing an IP address mapping for the queried name of the agent¹s choosing. In the second case, a third party operating an iterative resolver receives NXDomain responses generated by an authoritative name server and silently alters the contents, changing the non-existent name response to one that signals name exists and inserting an IP address mapping for the queried name of the third party¹s choosing. This behaviour is known by various labels: subdomain redirection, NXDomain redirection, NXDomain rewriting, NXDomain hijacking, subdomain hijacking, error resolution, and error marketing. These labels illustrate that the practice has commercial significance and is controversial. The aim of this presentation is to describe the effects of DNS response modification on domain name registrants, DNS operators and Internet users, and to explore possible exploitation of the practice by bad actors. The focus will be on explaining the effects of and unintended consequences to users, domain registrants, and those who rely on non-existent domain responses for error reporting and administrative purposes. Regards, Nick Ashton-Hart, Matthias Langenegger, Frederic Teboul ICANN At-Large Staff email: staff@atlarge.icann.org