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DNS-over-HTTPS Coming to Firefox

Mozilla this week announced plans to gradually roll-out DNS-over-HTTPS (DoH) in Firefox starting this month, though only users in the United States will receive it in the beginning.

Mozilla this week announced plans to gradually roll-out DNS-over-HTTPS (DoH) in Firefox starting this month, though only users in the United States will receive it in the beginning.

The DoH protocol was designed to enhance overall security of Internet users by sending DNS queries and getting DNS responses over HTTP using TLS security, which improves both integrity and confidentiality.

Mozilla first started working on the DoH protocol in 2017 and has been experimenting the protocol’s deployment in Firefox since June 2018. At the moment, over 70,000 users have already enabled DoH in their stable versions of Firefox, the browser maker says. 

The Internet organization also notes that experiments have demonstrated that their service is reliable and delivers good performance, that deployment problems can be detected and mitigated, and that most users will benefit from the greater protections of encrypted DNS traffic. 

“We feel confident that enabling DoH by default is the right next step. When DoH is enabled, users will be notified and given the opportunity to opt out,” Mozilla notes. 

What the browser maker has learned was that Firefox users in the United States rarely configured OpenDNS’ parental controls and Google’s safe-search feature (only 4.3% of users in the study did) and that 9.2% of users triggered a split-horizon heuristics (accessed websites had domains with non-public suffixes or domain lookups returned both public and private IP addresses).

Moving forth, Mozilla plans on deploying DoH in fallback mode, meaning that Firefox will fall back and use the default operating system DNS if domain name lookups using DoH fail or if heuristics are triggered. 

“This means that for the minority of users whose DNS lookups might fail because of split horizon configuration, Firefox will attempt to find the correct address through the operating system DNS,” the organization says. 

Firefox already detects when parental controls are enabled in the operating system, and DoH will be automatically disabled in those instances, to respect user choice. The same will apply if Firefox detects that enterprise policies have been set on the device.

“We’re also working with providers of parental controls, including ISPs, to add a canary domain to their blocklists. This helps us in situations where the parental controls operate on the network rather than an individual computer,” Mozilla says. 

Mozilla also notes that it plans on revisiting the use of canary domain and that it will pay close attention to how it is adopted, to learn if it isn’t being abused to disable DoH in situations where users have not explicitly opted in.

Related: Google Makes DNS Over HTTPS Generally Available

Related: Mozilla Brings Encrypted SNI to Firefox Nightly

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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