Adrozek Malware

Google Chrome, Firefox, Microsoft Edge, and Yandex have become the most recent targets of an ongoing malware campaign, called Adrozek, as disclosed by Microsoft.

The malware injects ads into search results and adds malicious browser extensions. The threat being noticed on above 30,000 devices each day.

How do Adrozek Malware works?

The main goal for Adrozek is to lead people to affiliated pages. The malware silently adds malicious browser extensions and changes browser settings to insert ads into webpages, often on top of legitimate ads from search engines. It also modifies the Dynamic Link Library (DLL) files per target browser, MsEdge.dll on Microsoft Edge, for instance, to turn off security controls.

The intended effect is for users, searching for certain keywords, to unintentionally click on these malware-inserted ads, which lead to affiliated pages. The attackers earn through affiliate advertising programs, which pay by the amount of traffic referred to sponsored affiliated pages.

Comparison of search results pages on an affected machine and one with Adrozek running

Distribution Infrastructure

Microsoft stated that from May to September, it recorded hundreds of thousands of encounters of the Adrozek malware globally. The company tracked 159 unique domains, each hosting an average of 17,300 unique URLs, which, in turn, host an average of over 15,300 distinct, polymorphic malware samples.

Microsoft expects the Adrozek operation to raise even more in the coming months.

Adrozek attack chain

Modifying browser components

Extensions

Adrozek makes changes to certain browser extensions. The Microsoft team noted this specifically on Google Chrome. It typically modifies the default “Chrome Media Router” extension. Similarly, on Microsoft Edge and Yandex Browser, it uses IDs of legitimate extensions, such as “Radioplayer”.

Browser DLLs

The malware also tampers with certain browser DLLs. For instance, on Microsoft Edge, it modifies MsEdge.dll to turn off security controls that are crucial for detecting any changes in the Secure Preferences file.

Browser security settings

Browsers have security settings that defend against malware tampering. The Preferences file, for example, contains sensitive data and security settings. Chromium-based browsers detect any unauthorized modifications to these settings through signatures and validation on several preferences.

Browser updates

To prevent the browsers from being updated with the latest versions, which could restore modified settings and components, Adrozek adds a policy to turn off updates.

Persistence

Adrozek changes several systems settings to have even more control of the compromised device. The ‘tag’ and ‘did’ entries contain the command-line arguments are used to launch the main payload. To maintain persistence, the malware creates a service named “Main Service”.

Ad injection

The injection of ads is performed by malicious scripts downloaded from remote servers. Depending on the search keyword, scripts add related ads at the top of legitimate ads and search results.

Credential theft

On Mozilla Firefox, malware downloads an additional randomly named .exe file, which steals device information and the currently active username and sends this information to the attacker.

Conclusion

Microsoft Defender Antivirus, the built-in endpoint protection solution on Windows 10, uses behaviour-based, machine learning-powered detections to block Adrozek. End users who find this threat on their devices are advised to re-install their browsers.

Configuring security software to automatically download and install updates, as well as running the latest versions of the operating system and applications and deploying the latest security updates help harden endpoints from threats.

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