Mitigating Infostealer Malware

Threat actors are increasingly using infostealer malware to infiltrate and exploit digital systems. Here's what you need to know.

Infostealer malware is a stealthy tool that enables attackers to harvest sensitive information. While malevolent in and of itself, this is often a precursor to a larger incident such as ransomware. In this post, we will delve into the concept of infostealer malware, its functionality, and how ransomware groups leverage it as a precursor to their nefarious activities.

Understanding Infostealer Malware

Infostealer malware is a type of malicious software designed with the primary goal of extracting valuable information from compromised systems. It discreetly infiltrates computers, operating in the background without arousing suspicion. Infostealers can target a range of data, including login credentials, financial information, personal identities, intellectual property, and more. The harvested information is collected by attackers and often sold to other threat actors who will use the data to conduct additional attacks.

Working Mechanism

Infostealer malware utilizes various sophisticated methods to carry out its data pilfering operations. Some common techniques employed by infostealers include:

1. Keylogging: Infostealers can log keystrokes to capture sensitive information such as passwords, credit card details, and other credentials entered by the user.
2. Form Grabbing: This technique involves intercepting data submitted through web forms, including online banking or e-commerce check-out pages.
3. Credential Theft: Infostealers can target stored login credentials saved in web browsers, email clients, or other applications, gaining access to user accounts.
4. Session Hijacking: By stealing session cookies from the browser, some infostealers enable attackers to bypass multifactor authentication, using the same session cookie to impersonate a user.
5. Screen Capture: Infostealers may take screenshots at regular intervals or upon specific triggers, providing attackers with a visual record of the victim's activities.

Infection Methodologies 

There are two primary ways that cybercriminals distribute infostealer malware: email attachments and drive-by downloads.

Email Attachments: Phishing emails are a common tactic used by cybercriminals to spread infostealer malware. These emails are designed to look legitimate and often contain attachments disguised as important documents, shipping notices, or invoices. Once the unsuspecting victim opens the attachment, the malware is unleashed onto their system, allowing it to quietly collect sensitive information.

Drive-by Downloads: Infostealer malware can also be delivered through compromised websites or malicious advertisements. When users visit these sites or click on infected ads, the malware is automatically downloaded onto their devices without their knowledge or consent. Outdated software or vulnerabilities in web browsers can make users particularly vulnerable to these types of attacks. It's crucial to stay vigilant and keep your software up-to-date to protect against these threats.

Ransomware and Infostealers

Cybercriminals behind ransomware campaigns have recognized the value of infostealer malware as a precursor to their malicious activities. Throughout the years, various ransomware groups have partnered with or purchased access proffered by infostealer operators. 

For example, the Conti ransomware group has been associated with the TrickBot infostealer. While the DoppelPaymer ransomware group was discovered to have connections with operators of Dridex. TrickBot and Dridex are two well-known infostealers that can steal sensitive information such as login credentials, financial information, and were leveraged for numerous ransomware attacks. More recently, ransomware groups such as Quantum and BlackCat have used Emotet, another infostealer, to gain access to victims.

Mitigating Infostealer Malware and Ransomware Threats

1. Email Security: Use a reliable email security provider to block any malicious email attachments that might contain infostealer malware.
2. Strong Multifactor Authentication (MFA): Enable strong multifactor authentication. Since many infostealers now steal session cookies it’s key to use modern phishing-resistant forms of MFA.
3. Endpoint Detection and Response (EDR): Deploy reputable EDR solutions to detect and block infostealer malware and subsequent malicious activities.