Infostealer Malware Fuels Ransomware Surge by Bypassing MFA Infostealer malware has emerged as a critical enabler of ransomware attacks, providing attackers with silent access to corporate networks by harvesting credentials, session cookies, and other sensitive data from infected devices. Unlike ransomware, which announces its presence, infostealers operate covertly, exfiltrating data to attacker-controlled servers without disrupting system functionality. The stolen data compiled into "stealer logs" is aggregated and sold by initial access brokers to ransomware affiliates. The most dangerous component of these logs is active session cookies, which allow attackers to hijack authenticated sessions without triggering multi-factor authentication (MFA). By importing stolen cookies into their browsers, threat actors inherit the victim’s authenticated state, bypassing passwords and MFA entirely. DarkOwl’s research highlights that session hijacking is one of several techniques used to defeat MFA, alongside push bombing and adversary-in-the-middle phishing. Verizon’s 2025 Data Breach Investigations Report found that 88% of web-application breaches involved stolen credentials, many sourced from infostealer logs reused in credential-stuffing attacks. Underground marketplaces, including Telegram groups and searchable "Underground Clouds of Logs," have streamlined the trade of stolen credentials, enabling even low-skilled attackers to acquire bulk data. In June 2026, a single collection of stealer logs contained 124 million unique passwords, underscoring the scale of this threat. Since stolen session tokens remain valid until revoked, organizations face persistent risks long after the initial infection. Incident responders recommend revoking active sessions before resetting passwords, as password changes alone fail to block attackers holding live tokens. With MFA adoption widespread, stolen session cookies have become the primary tool for ransomware affiliates to infiltrate enterprise networks undetected.