Internet-connected hosts are subject to constant probing and attacks from malicious actors. Brute-force attacks represent a large threat to account compromise for hosts and their networks.

Blocking brute-force attackers at the firewall level reduces system load and log noise, especially for high-traffic and deeply embedded systems.

Brute-force attacks Brute-force attacks without SSHGuard
Attacks are blocked SSHGuard blocks brute-force attacks

How Does SSHGuard Work?

Log Ingestion

SSHGuard monitors system log files and journal logs. It can work with multiple log sources, including:

  • cockpit
  • Common Log Format
  • macOS log
  • metalog
  • multilog
  • raw log files
  • syslog
  • syslog-ng
  • systemd journal

Attack Detection

SSHGuard parses logs for recognized attacks. Unlike other brute-force blockers, SSHGuard's parser is:

  • Fast. Attack signatures are compiled into a full lexical analyzer which does not slow down when more signatures are added.
  • Sandboxed. It runs as a separate, unprivileged, and sandboxed (where supported) process.
  • Secure. It is not susceptible to regular expression denial of service (ReDoS) attacks because signatures are compiled into a deterministic finite-state machine that does not exhibit unbounded behavior even with specially crafted inputs.


SSHGuard blocks repeat attackers using one of many firewall backends, including:

SSHGuard doesn't lock you out. By default, attackers are unblocked after a certain amount of time. But if you chose, you can configure blacklisting to block attackers permanently.

Functional spotlights

  • Touchiness and automatic blacklisting
  • Full IPv6 support
  • Monitors multiple log files
  • Small system footprint
  • Sophisticated whitelisting
  • Recognizes many logging formats transparently
  • Handles host names or addresses in log files

Non-functional spotlights

  • Easy to set up, simple one-line command to use
  • Written in small, portable C and Bourne shell with ~3000 LOC
  • Simple, extensible firewall interface