The Behavior of Coordinated SSH Brute Force Attacks over the last three months [Guest Diary], (Wed, Jun 17th)
Source SANS ISC Handlers Diary
Description
[This is a Guest Diary by Adam Nason, an ISC intern as part of the SANS.edu BACS program]
Impact
The impact is primarily the high volume of persistent SSH brute force attempts that increase the risk of unauthorized access if weak or default credentials are used. Although no specific vulnerability or exploit is described, the coordinated nature of these attacks can lead to successful compromises on poorly secured SSH servers, potentially resulting in unauthorized remote access. The attacks also impose resource consumption on targeted systems and networks. No known exploits in the wild or direct remote code execution vulnerabilities are confirmed in this data.
Defensive guidance
Recommended mitigations include disabling root user SSH login, enforcing multi-factor authentication (MFA), using properly protected and rotated private SSH keys, and hardening jump boxes. Network-level controls such as IP blocking, geo-blocking, and changing default SSH ports can reduce exposure. Deploying detection rules in SIEM or intrusion detection systems to alert on brute force patterns is advised. These measures effectively mitigate the risk posed by these brute force campaigns.
Summary
This report analyzes SSH brute force attack behavior observed via a DShield honeypot from February to May 2026. The honeypot logged over 20 million attempts, with attack volumes correlating closely with major geopolitical tensions and cybersecurity advisories. The data shows coordinated botnet-driven campaigns using a managed attack toolkit, evidenced by identical HASSH fingerprints and synchronized scanning bursts from multiple countries and ASNs. Attack rates were throttled and assigned by a controller, indicating organized botnet operations. The majority of brute force attempts targeted the 'root' user, a common SSH attack vector. The report emphasizes the adaptability and persistence of threat actors in response to external events but does not identify a specific exploitable vulnerability or known exploit in the wild.
References
Community reviews
Related threats
- CVE-2026-98432: Linux kernel IPv4 TCP use-after-free IssueHighVulnerability
- Swarming Against Citrix 0-Day ExploitationCampaign
- Fresh WordPress Vulnerability in Attackers’ CrosshairsHighVulnerability
- php2shell one week later: Why one exploit doesn’t work everywhereHighVulnerability
- ZDI-26-839: MLflow PickleEvaluationArtifact Deserialization of Untrusted Data Remote Code Execution VulnerabilityHighVulnerability