Google is hosting dozens of extensions in its Chrome Web Store that perform suspicious actions on the more than 4 million devices that have installed it and that the developer has taken pains to carefully conceal.

The extensions, which so far number at least 35, use the same code patterns, connect to some of the same servers, and require the same list of sensitive systems permissions, including the ability to interact with web traffic on all URLs visited, access cookies, manage browser tabs, and execute scripts. In more detail, the permissions are:

Tabs: manage and interact with browser windows
Cookies: set and access stored browser cookies based on cookie or domain names (ex., "Authorization" or "all cookies for GitHub.com")
WebRequest: intercept and modify web requests the browser makes
Storage: ability to store small amounts of information persistently in the browser (these extensions store their command & control configuration here)
Scripting: the ability to inject new JavaScript into web pages and manipulate the DOM
Alarms: an internal messaging service to trigger events. The extension uses this to trigger events like a cron job as it can allow for scheduling the heartbeat callbacks by the extension

These sorts of permissions give extensions the ability to do all sorts of potentially abusive things and, as such, should be judiciously granted only to trusted extensions that can’t perform core functions without them.

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