Edge, Chrome, and Firefox at Risk of Adrozek Modifier and Ad Injection

Microsoft users beware: the OS giant has recently discovered a new strain of malware dubbed Adrozek that modifies Firefox, Edge, Yandex, and Chrome browsers on Windows machines and injects ads into their search engine results.

What Happened

Last week Microsoft’s 365 Defender Research Team identified new browser modifiers that attack popular browsers and inject ads into search engine result pages. Microsoft reported that hundreds of thousands of computer systems are vulnerable to this malware.

According to DataBreachToday, “If not detected and blocked, Adrozek adds browser extensions, modifies a specific DLL per target browser, and changes browser settings to insert additional, unauthorized ads into web pages, often on top of legitimate ads from search engines, Microsoft says.”

The only way to mitigate the threat is to reinstall the browser from scratch after removing it completely.

Once installed, the browser modifiers redirect the browser to affiliate ads owned by the hackers with the goal of making money. 

DataBreachToday and Microsoft went on to explain, “Cybercriminals abusing affiliate programs is not new—browser modifiers are some of the oldest types of threats. The fact that this campaign utilizes a piece of malware that affects multiple browsers is an indication of how this threat type continues to be increasingly sophisticated. In addition, the malware maintains persistence and exfiltrates website credentials, exposing affected devices to additional risks.”

Additional Details

Microsoft has found that hackers have created 159 domains hosting more than 17,000 URLs that direct users to 15,000 malware installations. Threat assessors found Adrozek in May 2020 and continued to witness infections through September 2020. In August, the infections peaked at more than 30,000 affected devices.

In its report about the incidents, Microsoft noted, “While many of the domains hosted tens of thousands of URLs, a few had more than 100,000 unique URLs, with one hosting almost 250,000. This massive infrastructure reflects how determined the attackers are to keep this campaign operational.”

Additionally, Microsoft reported, “When run, the installer drops a .exe file with a random file name in the %temp% folder. This file drops the main payload in the Program Files folder using a file name that makes it look like a legitimate audio-related software. We have observed the malware use various names like Audiolava.exe, QuickAudio.exe, and converter.exe. The malware is installed like a usual program that can be accessed through Settings>Apps & features, and registered as a service with the same name.”

How is the Browser Infected

When someone visits a malware-infected URL owned by the scammers, the malware is installed on their device in what is known as a drive-by download. The malware creates a folder in Program Files named QuickAudio.exe to evade detection. 

Adrozek then changes browser settings and configuration files. Some browser add-ons are also affected, such as Google Chrome’s Media Router extension. 

Microsoft commented, “Despite targeting different extensions on each browser, the malware adds the same malicious scripts to these extensions. In some cases, the malware modifies the default extension by adding seven JavaScript files and one manifest.json file to the target extension’s file path. In other cases, it creates a new folder with the same malicious components.”

What makes it challenging to detect is the malware changes some of the browser’s DLLs, turning off security settings. Another more alarming aspect, according to DataBreachToday, is that “Next, since most browsers can detect any unauthorized modifications, the malware puts in place a two-byte patch that nullifies the integrity check, which makes the browser potentially more vulnerable to hijacking or tampering.” It also turns off browser updates, which could overwrite the malware and restore its normal functionality. 

Microsoft researchers also discovered that on the Mozilla Firefox browser, the malware takes it a step further and perpetrates credential theft and exfiltrates data to be used in ransomware or identity theft. “It downloads an additional randomly named .exe file, which collects device information and the currently active username. It sends this information to the attacker,” Microsoft added.

According to The Hacker News, “Adrozek shows that even threats that are not thought of as urgent or critical are increasingly becoming more complex.”

How to Avoid Being Affected by Adrozek

As part of their notice to consumers, Microsoft urged infected customers to remove those browsers and download a fresh install. They also advised taking measures to prevent malware infections, including using URL filtering programs like Microsoft Defender SmartScreen on Microsoft Edge. Some other suggestions to avoid being infected in the first place are:

• Keep Microsoft software up to date; this includes OS security patches and add-ons.
• Never install software from untrusted sources. Do not visit websites with insecure URLs.
• Be very cautious about clicking any links contained in an email or social media ads.
• Never download attachments in emails they might be phishing.
• Always check URLs to make sure they are valid.
• Keep good backups to restore your system if it does get infected.
• Install and use powerful antivirus-anti-malware software to keep an eye out for malicious files and downloads.