Your adblocker may have a potentially major traffic problem

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EasyList has been hit by a burst of highly unusual traffic that is proving to be a problem for the community-run project.

A after (opens in new tab) from AdGuard, and ad blocker which uses its own filter list, claimed that since EasyList is used by 99.9% of all ad blockers, most users of such tools will also be affected.

A filter list is a comprehensive list of pop-up ads, trackers, and the like that ad blockers use to determine what to block and what to filter through. EasyList’s variant is a simple text file hosted on its domain that the adblocker retrieves regularly for updates. However, the download would take more than five minutes, due to a 10-20 fold increase in daily traffic that started earlier this month.

Touch again

In its post, AdGuard stated that it had faced the same problem last year and hypothesized that it stems from certain browsing apps on Android devices in India. An obvious design flaw in these apps meant that they tried to access AdGuard’s filter list every time they boot (which is more common on Android devices), even if they were running in the background.

AdGuard’s solution was to block traffic from these browsers, but they claim they still spend over 100 TB of denied access pages per month.

No support for EasyList

However, AdGuard claims that EasyList’s problem is worse because unlike AdGuard, it can’t get support from its hosting site, CloudFlare, to block these requests. AdGuard believes this is due to it not having an Enterprise account, which is the highest level of subscription available for the service.

When EasyList contacted CloudFlare support, the email response stated that the increased traffic had caused the distributed denial of service (DDoS) mitigation, CloudFlare’s security protocol that the company claims intelligently filters and breaks large volumes of traffic into manageable chunks to prevent denial-of-service.

The email also stated that EasyList is violating the Terms of Service (ToS) as the company does not allow requests for text files. The company suggested that EasyList should move the file to a different subdomain to make it available to its users.

As a result, EasyList is throttled and no ad blocker can directly access its filter list. AdGuard believes that EasyList’s only option would be to change its domain name, as the broken browser apps will continue to trigger a DDoS as long as the original is still being used. However, it warns that this is not an easy process and would have a knock-on effect on the expected thousands of open source projects currently using EasyList.

Way forward

AdGuard states that all filter lists are hosted on its own domain, so users should not be affected.

Users of other software may also be fine, as they may have already switched to using a mirror domain from which to access EasyList. However, AdGuard warns that the faulty browsers may eventually pull this too and repeat the problem again.

Previously, AdGuard tried to contact the developers of one of the faulty browsers to let them know about the problem, but claimed that the problem got even worse after that – noting that there may be more faulty browsers.

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