Mozilla Introduces Mechanism to Hijack all DNS Traffic in the Name of Privacy

In September of 2019 Mozilla will begin releasing DNS over HTTPS (DOH) in Firefox via their Trusted Recursive Resolver (TRR) program. A primer on DNS Security.

The change is based on a theme we’ve heard before: a) the old protocols don’t take security and privacy into consideration, and b) there is the threat that people can see what you are searching.

This should sound familiar, we saw a similar campaign driven by Google with their #httpseverywhere campaign in 2014 – 2018.

In both instances, these organizations are trying to tackle fundamental flaws in the technology fabric we all depend on. The difference being in how the problem is being approached.

Technically speaking, I don’t have an issue with the idea of making DOH available. I do question whether a system level control should shift to the web layer. What gives me heart burn is with their implementation – they are enabling it ON by default, without asking the consumer. They are also partnering with CloudFlare as their default DOH service provider; this means every request you make on Firefox will go to a private organization that the consumer has not chosen. For me, this is a serious breach of trust by the organization that is waving the trust banner.

In contrast, Google’s implementation will be set OFF by default. It will also allow the user to choose the DOH provider of their choice.

Why Should You Care about Mozilla’s DOH Implementation

If you are someone that is responsible for controlling what happens on your network, you should care a lot. The default implementation by Mozilla is, for lack of a better word, a Virtual Private Network (VPN) that allows anyone using Firefox to bypass whatever controls exist on a network.

A few examples of what this means:

  • Let’s assume you are a school. You have 100’s of kids on your school WiFi. You have implemented your own DNS resolver to protect kids from malicious sites or to stop them from accessing pornographic, or obscene content. This new implementation will make it so that your kids can now bypass your web controls.
  • Let’s assume you are a parent. You worry about what your kids have access to when they are surfing the web. You deploy a network tool to help you control what they can and can’t access while inhibiting the way they interact on the web. This new implementation will make it so that your kids can now bypass your web controls.
  • Let’s assume you are addicted to porn. A very real problem. You deploy controls on your network to prevent yourself from accessing obscene content (something is sometimes uncontrollable for the afflicted). This new implementation will make it so that you can now bypass your own web controls.
  • Let’s assume you are security engineering inside an enterprise NOC. You are chartered with analyzing traffic to ensure malicious traffic is not coming, or out. This new implementation will allow anyone on your network to bypass whatever controls you might have in place.
  • Let’s assume you are a government that is trying to implement new regulations to hold ISP’s responsible for child pornography and other nefarious acts online. This new implementation would prevent this.

These are only a few, crude, examples meant to highlight the seriousness of the chosen deployment by Firefox.

What Can You Do About Mozilla’s Implementation

If you prefer to retain control of your network and not allow Mozilla to make default choices for you, you have a few options:

Option 1: Leverage a Network Content Filtering Service That Disables By Default

If you are a parent, school, or large organization you can use a cloud-based DNS content filtering service like CleanBrowsing to help mitigate this change.

If you are a large enterprise, you can signal to FireFox that you have specific controls in places and the DOH deployment should be disabled.

Network administrators may configure their networks as follows to signal that their local DNS resolver implemented special features that make the network unsuitable for DoH.

DNS queries for the A and AAAA records for the domain “” must respond with either: a response code other than NOERROR, such as NXDOMAIN (non-existent domain) or SERVFAIL; or respond with NOERROR, but return no A or AAAA records.

Make note of this very important caveat in their release notes: If a user has chosen to manually enable DoH, the signal from the network will be ignored and the user’s preference will be honored. Depending on your organizations position on this, you might want to consider Option 3.

Option 2: Disabling DNS-over-HTTPS in Firefox

You can disable DoH in your Firefox connection settings:

  1. Click the menu button  and choose Preferences.
  2. In the General panel, scroll down to Network Settings and click the Settings… button.
  3. In the dialog box that opens, scroll down to Enable DNS over HTTPS.
    • On: Select the Enable DNS over HTTPS checkbox. Select a provider or set up a custom provider.
    • Off: Deselect the Enable DNS over HTTPS checkbox.
  4. Click OK to save your changes and close the window.

Option 3: Remove Firefox

As extreme as an option as this might sound, I have spoken with a few enterprise CISO’s that are considering the option of removing Firefox from their network. Their reasoning revolves around two distinct positions: browsers assuming too much control and treating Firefox as a VPN. Which seems to be the direction they are intentionally heading.

The Evolution of a Critical Piece of the Web – DNS

A critical piece of the web is evolving and for most consumers you have no understanding or appreciation for what that means, but the implications can be dramatic.

Regardless of which side of the fence you’re on, there is a mutual desire amongst technologists to to ensure a more secure, private, web; the question, however, is how you implement it.

I’ll dive deeper into the specifics of the community politics, and technical details between the options, in future articles. If you absolutely can’t wait, I encourage you to read this great article by one of my colleagues at GoDaddy, Brian Dickson with our DNS team – DNS-over-HTTPS: Privacy and Security Concerns

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