Mitigating SSH brute-force threats on Linux systems
Locking the Gate
© Photo by Zoshua Colah on Unsplash
SSH brute-force attacks are still a major threat to Linux servers in 2025. Learn how to block them with key-only logins, Fail2ban, iptables, knockd, and more.
Brute-force attacks on Secure Shell (SSH) have existed for over a decade, yet they remain one of the most common and dangerous attack vectors on Linux systems today. In 2025, attackers are not guessing passwords manually; they are using automated botnets that scan and break into thousands of servers at a time with industrial speed.
One example is the recently discovered PumaBot, a botnet written in Go and designed specifically to infect Linux-based devices, including cloud virtual machines (VMs), personal servers, and even embedded systems. PumaBot uses SSH brute-force techniques to compromise devices and then links them together in a wider network, giving attackers access to computing power, storage, and Internet bandwidth for malicious purposes.
The botnet targets devices with open SSH ports and either weak or default credentials. Once a device is compromised, it can be used to launch further attacks, mine cryptocurrency, exfiltrate data, or deliver malware. With many people still using password-based logins for SSH, PumaBot and similar tools continue to succeed.
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