sshd: Invalid User in Auth Logs (SSH Brute Force Detection)
See real 'sshd: invalid user' strings in auth.log files. Detect automated SSH brute force attacks instantly and block the IPs before a breach occurs.
Log Signature Detected: If you're seeing "Apr 2 18:45:01 server sshd[12345]: Invalid user oracle from..." in your logs, your server may be under a Brute Force attack.
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Real Log Example
Apr 2 18:45:01 server sshd[12345]: Invalid user oracle from 203.0.113.50 port 49152
Apr 2 18:45:03 server sshd[12346]: Invalid user postgres from 203.0.113.50 port 49154
Apr 2 18:45:05 server sshd[12347]: Invalid user git from 203.0.113.50 port 49156Does your log look like this? Paste it into Helix Vanguard for instant AI analysis.
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What Is a Brute Force?
Security analysts and DevOps teams monitoring infrastructure like Nginx, Apache HTTP Server, Node.js, AWS, and WordPress must be able to quickly identify and triage these malicious log patterns to prevent data breaches.
The log string 'sshd: Invalid user' appears in your authentication logs when an incoming SSH connection attempts to log in with a username that does not exist.
A rapid sequence of these logs from the same IP address across different usernames is the definitive signature of a credential stuffing or dictionary attack.
Botnets continuously scan the internet for port 22, running through massive lists of default credentials hoping to find an exposed service account. To see how this looks from the web server side, review the failed password invalid user SSH logs.
How to Detect sshd: Invalid User in Auth Logs (SSH Brute Force Detection) in Logs
The Dictionary Pattern: Attackers use standard dictionaries. You will see sequential attempts for generic names: 'pi', 'ubuntu', 'oracle', 'tomcat', 'git', 'docker'.
Timing Cadence: Automated tools often execute exactly one login attempt every 1 to 3 seconds.
The Port Number: The port listed in the log (e.g., 'port 49152') is the ephemeral source port of the attacker, not the port your SSH server is listening on.
Brute Force Attack Detection Checklist
| Pattern | Indicator | Severity |
|---|---|---|
| Invalid user from same IP cycling names | SSH dictionary attack in progress | Critical |
| Attempts for pi, ubuntu, oracle, docker | Default credential dictionary | High |
| One login attempt every 1-3 seconds | Automated credential stuffing tool | High |
How to Defend Against This Threat
Completely disable password authentication for SSH and rely exclusively on SSH keys.
Install and configure Fail2Ban to monitor your auth logs and drop the attacker's IP.
Move your SSH service off the default Port 22 to a random high port.
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