Chromium Blog: ad blocking

Web Request and Declarative Net Request: Explaining the impact on Extensions in Manifest V3

Wednesday, June 12, 2019

The Story So Far As part of an effort to increase user security and privacy, Chrome is planning a number of changes to the extensions platform. We announced some of these changes last October, and have provided additional context on them today. These changes to the platform are being implemented as part of Manifest V3 – the next version of the Chrome Extensions platform.
One of these changes is to move away from the blocking version of the Web Request API towards a new API, called Declarative Net Request. There’s been a lot of confusion and misconception around both the motivations and implications of this change, including speculation that these changes were designed to prevent or weaken ad blockers. This is absolutely not the goal. In fact, this change is meant to give developers a way to create safer and more performant ad blockers.
In order to improve the security and privacy guarantees of the extensions platform, we are rethinking some of the extension platform's core APIs. That's why we're planning to replace the blocking Web Request API with the Declarative Net Request API.

How Web Request Works
With Web Request, Chrome sends all the data in a network request to the listening extension - including any sensitive data contained in that request like personal photos or emails. The extension has a chance to evaluate the request, and then tells Chrome what to do with the request: allow it, block it, or send it with some modifications. As a result, extensions that leverage the Web Request API typically have access to read and manipulate everything a user does on the web.

While this API is used by good actors to implement powerful features like content blockers, it can also be - and has been - abused. Because all of the request data is exposed to the extension, it makes it very easy for a malicious developer to abuse that access to a user’s credentials, accounts, or personal information. Since January 2018, 42% of malicious extensions use the Web Request API.
In addition to these safety concerns, there are also significant performance costs. In most cases, these costs are not from the evaluation of the extension script processing events, but rather from everything else coordinating the script. That overall performance impact can be very large, even for an extension written as performantly as possible where the JavaScript execution time is negligible.
As it’s designed today, the blocking version of the Web Request API requires a persistent, long-running process, and is fundamentally incompatible with “lazy” processes - processes that can be set up or torn down as-needed, conserving valuable system resources. There are also significant costs associated with the serialization of the request data, the inter-process communication needed to send that data to the extensions, and the processing of extension responses.

Enter Declarative Net Request
The Declarative Net Request API works differently than the Web Request API. Instead of Chrome sending all the information about a request to the listening extensions at the time of the request, extensions register rules that tell Chrome what to do if certain types of requests are seen.

This approach has advantages for both user security and privacy, as well as performance. With a declarative approach, Chrome does not need to expose any sensitive data to the extension. The browser can perform the action requested by the extension without sending it all the data associated with the network request, because the extension already specified the conditions under which different actions are taken. This enables the extension to perform content blocking without needing access to all of a user’s personal information.
This has significant performance implications. Most importantly, a persistent, long-running process is no longer necessary because rules are registered before requests are made rather than needing to process them at runtime. This also cuts down on the cost of serializing all the request data and shuttling the inter-process messages to the listening extensions. These performance improvements will make extensions significantly more viable on resource-constrained platforms.

Why Not Both? In addition to the performance concerns raised above, the Chrome team strongly believes that users should not have to expose their emails, photos, social media, or any other sensitive data to an extension if the extension doesn’t actually need that access to perform its function. And historically, when extension developers are given the choice between capability and security, the vast majority of developers choose capability. We've seen this repeatedly on the extensions platform with event pages, optional permissions, and activeTab.

Enterprise Enterprises, schools, and businesses often require different network and software controls to comply with corporate policies. Additionally, these organizations typically have administrators whose role it is to understand and set up their environments.
Chrome provides enterprise controls through its administrator policies. The blocking version of the Web Request API remains available for managed extensions because of the deep integrations that enterprises may have between their software suites and Chrome. System administrators can continue to manage Chrome in enterprise environments for free using OS-provided mechanisms to deploy Chrome policies.

Moving Forward Declarative Net Request, and the whole of Manifest V3, is still very much in design and development. We are continuing to iterate on it, responding to community feedback and working with developers to help support different use cases.
Since the original announcement of the Declarative Net Request API, we have added significant functionality to the API as a result of these discussions. The Declarative Net Request API now allows for the registration and removal of dynamic rules - specified at runtime rather than statically in the manifest. We’ve also added the capability to remove common tracking headers, such as Referer, Cookie, and Set-Cookie.
We are actively exploring other ways to expand this API, including adding methods to get feedback about matched rules, and support for richer redirects leveraging URL manipulation and regular expressions. Additionally, we are currently planning to change the rule limit from maximum of 30k rules per extension to a global maximum of 150k rules.
We will continue working with the developer community moving forward. We understand that adopting Manifest V3 will require developers to update their extensions and we will continue to support them through this transition.

Posted by Simeon Vincent, Developer Advocate for Chrome Extensions

Building a Better World Wide Web

Wednesday, January 9, 2019

User experience sits at the core of everything we do at Google. It drives our product decisions, development and direction. Chrome has a long history of protecting our users from annoying and harmful experiences -- like blocking pop-up windows and warning users if a page has malware.
We’ve also taken action to protect Chrome users from certain types of advertising that diminish their experiences online, a common complaint among Chrome users. For example, last year, Chrome began filtering ads on sites in North America and Europe that repeatedly violate industry standards and continue to show intrusive, annoying ads to people that visit their websites. Further, our own advertising platforms have stopped selling the kinds of ads that violate these standards and generate complaints from Chrome users.
We follow the Better Ads Standards when determining which websites to filter ads on in Chrome. These standards were developed by the Coalition for Better Ads, an industry group dedicated to improving the web advertising experience, based on feedback from over 66,000 consumers around the world. The Standards identify 12 experiences that users find intrusive and that advertisers, publishers, and technology vendors should avoid showing.

Today, the Better Ads Standards consists of 12 ad experiences that research found to be particularly annoying to users. Image Source: Coalition for Better Ads
Today, the Coalition for Better Ads announced that it is expanding their initial Better Ads Standards beyond North America and Europe to cover all countries, worldwide. Following the Coalition’s lead, beginning July 9, 2019, Chrome will expand its user protections and stop showing all ads on sites in any country that repeatedly display these disruptive ads.
What does this mean for website owners? If you operate a website that shows ads, you should consider reviewing your site status in the Ad Experience Report, a tool that helps publishers to understand if Chrome has identified any violating ad experiences on your site. Starting today, publishers in regions outside of North America and Europe can use this tool to understand if they have intrusive ad experiences on their site, their current status (passing / no issues found or failing), and resolve outstanding issues or contest a review. While we’ve already reviewed millions of sites around the world, we will continue to expand these reviews in the coming months.
A quick overview of the Ad Experience Report.
Early results from the U.S., Canada and Europe Our ultimate goal is not to filter ads, but to build a better web for everyone, everywhere. Chrome's enforcement of the Coalition’s standards has inspired many website owners to improve the advertising experience on their sites in a way that benefits users. In the U.S., Canada, and Europe, website owners have successfully been able to make changes to the ads on their sites. As of January 1, 2019, two thirds of all publishers who were at one time non-compliant to the Better Ads Standards are now in good standing. Further, out of millions of sites we’ve reviewed to date, less than 1% have had their ads filtered.
We look forward to continued collaboration with the industry to create a better, more vibrant web ecosystem with only the best user experiences. The web is a critical part of our everyday life and we’ll continue to deliver the best user experiences.
You can learn more details from the Coalition here.
Posted by Ben Galbraith, Senior Director of Product, Chrome

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Web Request and Declarative Net Request: Explaining the impact on Extensions in Manifest V3

Building a Better World Wide Web

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