AllBlock malicious ad blocker injects new ads into browser

Experts from Imperva discovered the malicious ad blocker AllBlock, a browser extension, which fulfills its task, also but injects hidden affiliate links into the browser.

The extension is still available in the Chrome Web Store and is positioned as a tool for blocking ads on YouTube and Facebook, including to combat pop-ups and speed up browsing.

Researchers say AllBlock indeed fights advertising, but only to implement its own. For example, AllBlock forces legitimate URLs to redirect users to affiliate links controlled by the extension’s developers.

Specialists discovered the strange AllBlock activity back in August 2021, when they identified a number of previously unknown malicious domains distributing a script to inject ads. The script sent legitimate URLs to the remote server and received a list of domains to redirect in response. If a user clicked on a link modified in this way, he was redirected to another page (usually an affiliate link).

In addition, the script can evade detection, for example, stays out of sight of large search engines, clears the debug console every 100 ms and actively detects Firebug variables.

After examining the AllBlock blocker in more detail, the Imperva team discovered this script (bg.js), which injects the code into each new tab opened in the browser. To inject a malicious script, the extension connects to a URL on allblock.net, which returns the script in base64, after which it will be decoded and embedded into the page. At the same time, the developers of the extension even added several harmless objects and variables to the malicious code fragment, trying to hide its malicious functions.

Let me remind you that Strange malware prevents victims from visiting pirate sites.