What are Stealer Logs?

Stealer logs are structured data archives produced by infostealer malware after infecting a device. Each log is a compressed package containing what the malware extracted from the victim’s machine: saved browser passwords, session cookies, autofill data, cryptocurrency wallet files, and system information.

According to the Verizon 2025 Data Breach Investigations Report, credentials were involved in 88% of basic web application attack breaches, and 54% of ransomware victims had their domains appear in infostealer credential dumps. In 2025, infostealer activity exposed 1.8 billion credentials globally. IBM X-Force recorded an 84% year-over-year increase in infostealers delivered via phishing in 2024.

Anatomy of a Stealer Log

The System_Info.txt file is particularly useful for targeted follow-on attacks. It tells attackers what security tools are installed, the machine’s hardware fingerprint, and how to tailor further activity to avoid detection.

How Stealer Logs Reach the Dark Web

Infection: Infostealers spread primarily through phishing emails, malvertising, cracked software, and fake software updates. Widely deployed families include LummaC2, RedLine, and Vidar. LummaC2 alone accounted for 23.3 million detections globally in 2025 according to the Identity Threat Report 2025.

Exfiltration: The malware collects data silently and sends it to the attacker’s server, typically within minutes of infection.

Distribution: Telegram is the primary distribution channel in 2025, with automated channels providing bulk logs. Dark web marketplaces such as Russian Market are also major distribution points. Infostealers are sold under a malware-as-a-service (MaaS) model, with an average subscription cost of approximately $200 per month in 2024.

Why Stealer Logs Bypass MFA

Stolen session cookies enable a technique called a pass-the-cookie attack, which bypasses multi-factor authentication entirely.

When you log in to a website and complete MFA, your browser stores a session cookie confirming your device has authenticated. An attacker who obtains that cookie through a stealer log can import it into their own browser. The target website sees a valid session and grants access with no password prompt and no MFA challenge.

Microsoft’s documentation confirms that session cookies such as ESTSAUTH can persist until explicit logout or expiration, potentially enabling weeks of undetected access. Recorded Future has tracked thousands of underground forum references to pass-the-cookie and session hijacking techniques. A more recent evolution called Cookie-Bite uses browser extensions to continuously extract fresh session cookies each time a victim authenticates, maintaining long-term persistent access.

How to Detect and Respond

For security teams:

• Deploy Dark Web monitoring to receive alerts when your organization’s domains or employee credentials appear in newly circulating log dumps
• Implement Identity Threat Detection and Response (ITDR) platforms that flag anomalous session behavior such as a session cookie used from a new geography or unfamiliar device
• Shorten session token validity windows and enforce re-authentication for high-privilege actions
• When an employee device’s hardware ID appears in a known log, trigger immediate forced logout and credential resets
• EDR tools can detect infostealer behavior patterns such as mass browser database reads and rapid file compression

For individuals:

• Use a password manager rather than saving credentials in your browser
• Clear browser cookies regularly, especially on shared or public devices
• Review active sessions in account security settings and terminate any you do not recognize
• Check your email at haveibeenpwned.com for known breach exposure

Key Takeaways

• Stealer logs are the output of infostealer malware, capturing passwords, session cookies, system info, and more
• In 2025, 1.8 billion credentials were exposed through infostealer activity; 54% of ransomware victims had prior infostealer infections
• Logs are distributed primarily through Telegram and dark web markets under MaaS subscription models
• The pass-the-cookie attack, enabled by stolen session cookies, bypasses MFA completely and is actively used
• SOC teams should combine dark web monitoring, ITDR, shortened session lifetimes, and EDR to reduce exposure