Over 20 million SSH brute force attempts hit my honeypot in 100 days, and the timing lines up exactly with war and vulnerability disclosures.
On February 25, CISA published Emergency Directive 26-03 for Cisco SD-WAN flaws. Within days, my Raspberry Pi running DShield saw a 2100% spike in SSH probing. That same week, US and Israeli strikes on Iran kicked off, and botnets clearly took notice.
300,000 Daily Probes and a 53-Second Coordinated Attack
March 8 recorded over 300,000 SSH brute force attempts in a single day - the peak of a sustained campaign that kept daily counts above 50,000 for two months. When the Iran ceasefire started in mid-April, activity dropped 95%, only to rebound in early May after CISA added a major Linux vulnerability to its catalog.
The coordinated nature of these attacks is undeniable. I found two probes from different IPs in the US and Ukraine happening within 53 seconds, sharing the same HASSH fingerprint (03a80b21afa810682a776a7d42e5e6fb) and SSH version. That fingerprint appeared in 702,706 events - a single managed attack toolkit deployed globally. DigitalOcean and M247 ASNs dominate the top ten probing IPs, with synchronized bursts suggesting a botnet controller assigning scan quotas per zombie.
What Stops These Attacks: Root Login and Default Ports
Over 20 million attempts in 100 days, and the vast majority targeted the 'root' user. Disabling root SSH login alone would have neutered nearly every one of these attacks. That's not a sophisticated defense - it's a configuration change most sysadmins can make in 30 seconds.
Geofencing, MFA, and SSH key authentication (properly rotated) would further shrink the attack surface. The data proves opportunistic botnets react to external events within hours, but they don't adapt well to basic hardening. They keep trying the same defaults because those defaults still work.
Next time you see a CISA alert about a Cisco or Linux flaw, expect a wave of SSH scans within 48 hours. If you haven't disabled root login and changed your SSH port yet, consider this your wake-up call.
Source: The Behavior of Coordinated SSH Brute Force Attacks over the last three months [Guest Diary], (Wed, Jun 17th)
Domain: isc.sans.edu
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