Google’s Chrome changes make life harder for ad blockers

Despite protests, Google is rolling out changes in the Chrome browser that make it harder for ad blockers to do their job.

Starting last Monday, June 3, 2024, Chrome Beta, Dev, and Canary channels will see the effects of the implementation of the new extension platform Manifest V3. The gradual disabling of V2 extensions will later follow for all Chrome users.

For those not familiar with the terms, Manifest V2 and V3 are the “rules” that browser extension developers are required to follow if they want their extensions to get accepted into the Google Play Store.

Manifest V2 is the old model. The Chrome Web Store no longer accepts Manifest V2 extensions, but browsers can still use them. For now. Google explained that the goal of the new extension platform:

“Is to protect existing functionality while improving the security, privacy, performance and trustworthiness of the extension ecosystem as a whole.”

That’s commendable, because it stops criminals from hiding the malicious intentions of their extensions when they submit them for the Google Play Store.

However, the part of the transition that hinders ad blockers lies in the fact that extensions will now have limitations on how many rules they include. Google has made some compromises after initial objections, but the limitations are still present and have a large effect on ad blockers since they historically rely on a large number of rules. That’s because, generally speaking, each blocked domain or subdomain is one rule, and cybercriminals set up new domains by the dozen.

Google has tried to address developers’ concerns by adding support for user scripts and increasing the number of rulesets for the API used by ad blocking extensions. But this might not be enough.

Users can temporarily re-enable their Manifest V2 extensions, but this option will eventually disappear.

One of the affected ad blockers is the one incorporated in our own Malwarebytes Browser Guard.

We talked to one of the developers about the plans for Browser Guard and how it will deal with the Manifest V3 rules. They told us that the new Browser Guard, which is already available in beta, will use a mix of static and dynamic rules to protect our users.

Static rules are rules that are contained in the ruleset files which can be seen as block lists. These files are declared in the manifest file.

Dynamic rules are rules that can be added and removed at runtime. Chrome allows up to 30k dynamic rules. Browser Guard uses dynamic rules for two purposes:

Session rules are dynamic rules that can be added and removed at runtime, but they are session-scoped and are cleared when the browser shuts down and when a new version of the browser is installed. And dynamic rules can be used to store allow lists, user blocked content, and general rules that block more than one domain. Take, for example, the IP address of a server that is known to host nothing but phishing sites.

And, to deal with urgent situations, we can use ruleset overrides, which are a mechanism by which we can override the static rules shipped with Browser Guard without requiring our users to add exclusions.

If you want to help Malwarebytes get ready for the transition, you can test the beta version of Browser Guard for Manifest V3.

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