Shieldlist

ssh Free

SSH brute force — wrong passwords, connections dropped in authentication, invalid banners; one jail

Category
ssh
Threshold
3/5m, 10/6h
Ban policy
ssh
Report
ssh-brute-force
Parsers
ssh-auth-fail ssh-preauth-abort ssh-auth-abandoned ssh-auth-timeout ssh-banner-invalid

Why it is written this way

SSH brute force — the one jail for sshd, whichever way it words a failed
attempt: a wrong password (a host that takes passwords), a connection
dropped or reset in authentication (the only trace a key-only host
writes), or a client that never got past the banner. One event, one
hit: the "Invalid user" line is NOT scored — the same attempt writes a
Failed password (or a preauth close) right after it. A connection that
tries N passwords then drops counts N+1: the tries and the drop.

Thresholds are the point: a brute force is judged over time, not ten
minutes — the short window catches the loud one (3 in 5 minutes), the
long one the patient one (10 in six hours). Nobody legitimate fails
three times in five minutes on a server they administer.

The rule file View raw

# SSH brute force — the one jail for sshd, whichever way it words a failed
# attempt: a wrong password (a host that takes passwords), a connection
# dropped or reset in authentication (the only trace a key-only host
# writes), or a client that never got past the banner. One event, one
# hit: the "Invalid user" line is NOT scored — the same attempt writes a
# Failed password (or a preauth close) right after it. A connection that
# tries N passwords then drops counts N+1: the tries and the drop.
#
# Thresholds are the point: a brute force is judged over time, not ten
# minutes — the short window catches the loud one (3 in 5 minutes), the
# long one the patient one (10 in six hours). Nobody legitimate fails
# three times in five minutes on a server they administer.
rule: ssh
description: SSH brute force — wrong passwords, connections dropped in authentication, invalid banners; one jail
category: ssh
parsers:
  - ssh-auth-fail
  - ssh-preauth-abort
  - ssh-auth-abandoned
  - ssh-auth-timeout
  - ssh-banner-invalid
# levels are the machine's now — strict halves these numbers, lenient doubles them, instant is the first hit; this rule declared strict: [3/10m, 8/1h, 15/6h]; lenient: [6/10m, 15/1h, 30/6h]
threshold: [3/5m, 10/6h]
ban: ssh
report: ssh-brute-force