A four-year study conducted by researchers at the University of Utah has revealed a significant increase in the frequency and sophistication of brute-force attacks against SSH servers. These cyberattacks target internet-connected systems, with attackers attempting to gain unauthorized access to servers, routers, IoT devices, and more. The researchers analyzed over 427 million failed SSH login attempts across more than 500 servers on CloudLab, a public cloud platform used by academic researchers worldwide.
The findings highlight the evolving tactics used by attackers, with a notable shift in recent years from targeting common administrator usernames like “root” and “admin” to usernames associated with cloud service images, network devices, IoT products, and specific software packages.
The study also revealed a wide diversity of attacker behaviors and persistence levels. While over half of the attacks came from IP addresses that disappeared within 24 hours, some attackers persisted in their efforts for months or even years. The researchers developed a defensive technique called Dictionary-Based Blocking (DBB) to counter these attacks. By analyzing the username dictionaries used by attackers, DBB can block 99.5% of brute-force attacks while allowing legitimate user access.
When evaluated against the industry-standard Fail2ban tool, DBB achieved significantly higher blocking rates while reducing false positives by 83%. The research underscores the importance of secure practices like using key-based authentication and strong passwords, and highlights the need for novel defensive approaches to maintain a safe internet ecosystem.
