Malicious Chrome Plugin Let Remote Attacker Steal keystroke and Inject Malicious Code

Researchers at Zimperium zLabs recently identified a new Chrome browser botnet called ‘Cloud9’ that is intent on stealing the following information using malicious extensions:-

• Online accounts credentials
• Log keystrokes
• Inject ads
• Inject malicious JS code
• Enroll the victim’s browser in DDoS attacks

This method is becoming increasingly attractive for malware developers to target web browsers as they contain the most valuable information about a user.

In the course of everyday activities, we can find out a lot about ourselves through our keystrokes or session cookies. A breach of security or a violation of privacy can be caused by having access to such information.

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Cloud9 botnet is a RAT that affects all Chromium-based web browsers, which are popular among consumers like Chrome and Microsoft Edge. Moreover, threat actors could exploit this RAT to remotely execute arbitrary commands.

Technical Analysis

The official Chrome web store doesn’t host this malicious Chrome extension, so it cannot be downloaded from there. 

The distribution channel of this malware relies on communities that are operated by threat actors, wherein the malware will be hidden by users of the tool before it gets delivered to the victims by the tool itself.

In terms of the Javascript files that make up the extension, there are only three. While the primary functionality of the extension can be located in a file called “campaign.js” which contains most of its functionality.

According to the report, During the initialization of campaign.js, the window.navigator API is used to identify the system’s operating system. Once the target has been identified, a Javascript file is injected into the victim’s computer system as a method to mine cryptocurrency using the resources of the victim’s computer system.

Next, for further proceedings, it injects another script known as cthulhu.js which comprises a full-chain exploit for the following flaws:-

• CVE-2019-11708 (Firefox)
• CVE-2019-9810 (Firefox)
• CVE-2014-6332 (Internet Explorer)
• CVE-2016-0189 (Internet Explorer)
• CVE-2016-7200 (Edge)

As soon as the vulnerabilities are exploited, Windows malware is automatically installed on the host machine and executed. This gives attackers even more opportunities to compromise systems and carry out even more severe malware attacks.

While one of the sophisticated inclusion of this malware is “Clipper,” a module that keeps scanning the clipboard of the system for copied data like:-

• Passwords
• Credit cards details

In addition to injecting ads into webpages silently, Cloud9 is also capable of generating revenue for its operators by generating ad impressions.

Cloud9 Botnet Functionalities

There are several key functionalities of this malware that can be abused by threat actors for malicious purposes, and here below we have mentioned all its functionalities:-

• Send GET/POST requests, which can be used to get malicious resources.
• CookieStealing, which can compromise user sessions.
• Keylogging, which could be used to steal passwords among other things.
• Layer 4 / Layer 7 hybrid attack, used to perform DDoS attacks from the victim’s PC.
• OS and Browser detection, for next-stage payloads
• Open Pop-unders, used to inject ads.
• Execute JavaScript Code from other sources, used to inject more malicious code.
• Silently load webpages, used to inject ads or to inject more malicious code.
• Mine cryptocurrencies on the browser, to use the victim’s computer resources to mine cryptocurrency.
• Send browser exploit, used to take control of the device by executing malicious code in the device.

As of right now, it is unknown how many victims have been affected by this incident. However, evidence indicates that the victims and attack scope of the malware is not limited since there is no specific web browser or country that is targeted by the malware.

Several of the C2 domains used in the recent campaign were also used in attacks launched by the Keksec malware group in the past, which suggests that the hackers behind Cloud9 have ties to them.

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