What is an Infostealer?

Infostealer Explained

An infostealer is a category of malware engineered to extract sensitive data from compromised systems, including saved passwords, browser cookies, session tokens, cryptocurrency wallet keys, and autofill form data. Unlike ransomware that announces its presence with encryption demands, infostealers operate silently, often completing data exfiltration within seconds of execution. The stolen data is packaged into structured bundles called "logs" and sold on dark web marketplaces, where buyers use them for account takeover, credential stuffing, session hijacking, and initial access for larger intrusions.

The infostealer threat has grown rapidly. In 2024, infostealers were responsible for nearly two-thirds of the 3.2 billion credentials stolen across all organizations, according to Flashpoint research. The FBI and CISA issued a joint advisory in May 2025 specifically addressing the LummaC2 infostealer's impact on U.S. critical infrastructure sectors.

How Infostealer Malware Works

Infostealers follow a consistent operational pattern mapped across several MITRE ATT&CK techniques:

1. Delivery. The malware arrives through phishing emails with malicious attachments, links to trojanized software downloads, or social engineering lures such as fake CAPTCHA pages (sometimes called "ClickFix" or "paste-and-run" attacks) that trick users into executing malicious commands.

1. Execution and harvesting. Once running, the infostealer targets browser password stores (T1555.003), session cookies (T1539), cryptocurrency wallet files, email client credentials, VPN and RDP configurations, and system fingerprint data. Many families complete this entire harvesting cycle in seconds.

1. Exfiltration. Harvested data is compressed and transmitted to attacker-controlled command-and-control infrastructure, typically over HTTPS to blend with normal traffic.

1. Monetization. Operators package stolen data into "logs" (one log per infected machine) and sell them on dark web markets and Telegram channels. Logs containing valid corporate credentials command premium prices on underground markets, with value scaling based on the target organization and level of access.

Major Infostealer Families

The infostealer landscape is dominated by malware-as-a-service (MaaS) platforms that provide subscribers with prebuilt tools, dashboards, and even customer support:

• Lumma (LummaC2). Specializes in credential and session token theft. First sold on Russian-language cybercriminal forums in 2022, Lumma became the subject of a CISA joint advisory in 2025 due to its impact on critical infrastructure.
• RedLine. One of the most widely deployed infostealers, responsible for 43% of all infostealer infections tracked by Flashpoint in 2024. Targets browser credentials, autofill data, and credit card information.
• Vidar. Focuses on browser passwords, cookies, autofill data, and cryptocurrency wallet information. Frequently distributed through malvertising and SEO-poisoned search results.
• Raccoon. Promoted through SEO-poisoned websites offering "free" or cracked software. Harvests credentials from multiple browsers and applications.
• StealC. A newer entrant that, combined with Lumma and RedLine, accounted for 75% of the 4.3 million machines infected by infostealer malware in 2024.

Why Infostealer Attacks Matter

Infostealers sit at the beginning of the attack chain for many larger compromises. Stolen session cookies allow attackers to bypass multi-factor authentication entirely, since the authenticated session is already established. Research indicates that over 54% of ransomware victims in 2024 and 2025 had their domain credentials appear on infostealer log marketplaces before the ransomware attack occurred. This makes infostealer infections an early warning indicator for email account compromise, lateral movement, and data breaches.

Organizations can reduce exposure by deploying email security that detects malicious attachments and links before delivery, enforcing endpoint protection with behavioral analysis, rotating credentials regularly, and monitoring dark web markets for exposed employee credentials.

Infostealer Protection from IRONSCALES

IRONSCALES detects infostealer delivery attempts by analyzing email attachment behavior and link patterns associated with malware distribution campaigns.

Related Terms

• Credential Harvesting
• Account Takeover
• Dark Web Monitoring
• Spyware
• Ransomware