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Query String Filter
The Brave query string filter aims at preventing the tracking of individual users without interfering with campaign-level tracking. We target parameters which are known to be specific to:
- a user,
- an email address, or
- an individual click.
This kind of tracking is typically used in cookie syncing, that is the practice of synchronizing the value of first-party cookies on different domains, or in tying clicks inside an email message to a website visit.
The way that the filter works is that we remove from the query string any parameters (i.e. the parameter name and its value) before we proceed with a network request. This means that such parameters never make it to the server, URL bar or the Referer header, and cannot be recovered by scripts running on a page.
A notable exception to this intervention is the unsubscribe link in emails. If a user-identifying tracking parameter is required for that functionality to work, we make an exception.
All issues related to this feature are tagged with the privacy/query-filter label.
The current list of parameters we filter can be seen in brave/browser/net/brave_site_hacks_network_delegate_helper.cc::GetQueryStringTrackers().
There is a test page at https://fmarier.github.io/brave-testing/query-filter.html.