Los spammers están ejecutando ataques de fuerza bruta para adivinar contraseñas en mi servidor (postfix en Debian). Ya adivinaron las contraseñas de dos usuarios y comenzaron a enviar spam usando mi servidor. Se cambiaron las contraseñas y se mitigaron los ataques (por ahora), pero quiero bloquearlos por completo.
Instalé fail2ban, pero por alguna razón no detecta los ataques.
/etc/fail2ban/fail.confcontiene:
[sasl]
enabled = true
port = smtp,ssmtp,submission,imap2,imap3,imaps,pop3,pop3s
filter = sasl
# You might consider monitoring /var/log/mail.warn instead if you are
# running postfix since it would provide the same log lines at the
# "warn" level but overall at the smaller filesize.
#logpath = /var/log/mail.log
logpath = /var/log/mail.warn
/etc/fail2ban/filter.d/sasl.confcontiene:
# Fail2Ban configuration file
#
# Author: Yaroslav Halchenko
#
# $Revision$
#
[Definition]
# Option: failregex
# Notes.: regex to match the password failures messages in the logfile. The
# host must be matched by a group named "host". The tag "<HOST>" can
# be used for standard IP/hostname matching and is only an alias for
# (?:::f{4,6}:)?(?P<host>[\w\-.^_]+)
# Values: TEXT
#
failregex = (?i): warning: [-._\w]+\[<HOST>\]: SASL (?:LOGIN|PLAIN|(?:CRAM|DIGEST)-MD5) authentication failed(: [ A-Za-z0-9+/]*={0,2})?\s*$
# Option: ignoreregex
# Notes.: regex to ignore. If this regex matches, the line is ignored.
# Values: TEXT
#
ignoreregex =
Cuando ejecuto el filtro /var/log/mail.warn, produce resultados:
# fail2ban-regex /var/log/mail.warn '(?i): warning: [-._\w]+\[<HOST>\]: SASL (?:LOGIN|PLAIN|(?:CRAM|DIGEST)-MD5) authentication failed(: [ A-Za-z0-9+/]*={0,2})?\s*$'
Running tests
=============
Use regex line : (?i): warning: [-._\w]+\[<HOST>\]: SASL (?:LOGIN|P...
Use log file : /var/log/mail.warn
Results
=======
Failregex
|- Regular expressions:
| [1] (?i): warning: [-._\w]+\[<HOST>\]: SASL (?:LOGIN|PLAIN|(?:CRAM|DIGEST)-MD5) authentication failed(: [ A-Za-z0-9+/]*={0,2})?\s*$
|
`- Number of matches:
[1] 15293 match(es)
Ignoreregex
|- Regular expressions:
|
`- Number of matches:
Summary
=======
Addresses found:
[1]
123.169.7.222 (Sun Feb 25 06:40:18 2018)
123.169.7.222 (Sun Feb 25 06:40:21 2018)
...
185.173.176.157 (Fri Mar 02 10:12:46 2018)
185.173.176.157 (Fri Mar 02 10:13:15 2018)
185.173.176.157 (Fri Mar 02 10:13:43 2018)
185.173.176.157 (Fri Mar 02 10:14:11 2018)
185.173.176.157 (Fri Mar 02 10:14:41 2018)
185.173.176.157 (Fri Mar 02 10:15:13 2018)
185.173.176.157 (Fri Mar 02 10:15:42 2018)
185.173.176.157 (Fri Mar 02 10:16:13 2018)
185.173.176.157 (Fri Mar 02 10:16:42 2018)
185.173.176.157 (Fri Mar 02 10:17:10 2018)
Date template hits:
34294 hit(s): MONTH Day Hour:Minute:Second
0 hit(s): WEEKDAY MONTH Day Hour:Minute:Second Year
0 hit(s): WEEKDAY MONTH Day Hour:Minute:Second
0 hit(s): Year/Month/Day Hour:Minute:Second
0 hit(s): Day/Month/Year Hour:Minute:Second
0 hit(s): Day/Month/Year Hour:Minute:Second
0 hit(s): Day/MONTH/Year:Hour:Minute:Second
0 hit(s): Month/Day/Year:Hour:Minute:Second
0 hit(s): Year-Month-Day Hour:Minute:Second
0 hit(s): Year.Month.Day Hour:Minute:Second
0 hit(s): Day-MONTH-Year Hour:Minute:Second[.Millisecond]
0 hit(s): Day-Month-Year Hour:Minute:Second
0 hit(s): TAI64N
0 hit(s): Epoch
0 hit(s): ISO 8601
0 hit(s): Hour:Minute:Second
0 hit(s): <Month/Day/Year@Hour:Minute:Second>
Success, the total number of match is 15293
However, look at the above section 'Running tests' which could contain important
information.
A pesar de todo eso, /var/log/fail2ban.logno muestra el bloqueo de la dirección IP infractora.
Actualizar
Siguiendo las sugerencias, incrementé el nivel de registro. Esta espectáculos:
2018-03-02 12:47:55,920 fail2ban.filter : DEBUG Processing line with time:1519986602.0 and ip:185.173.176.157
2018-03-02 12:47:55,920 fail2ban.filter : DEBUG Ignore line since time 1519986602.0 < 1519987675.92 - 600
2018-03-02 12:47:55,920 fail2ban.filter : DEBUG Processing line with time:1519986635.0 and ip:185.173.176.157
2018-03-02 12:47:55,920 fail2ban.filter : DEBUG Ignore line since time 1519986635.0 < 1519987675.92 - 600
El jail.conf tiene:
bantime = 600
maxretry = 3
Respuesta1
Del Ignore line since time 1519986602.0 < 1519987675.92 - 600registro de registro ylos documentos, supongo que ese 600es el valor de la findtimeopción. Es decir, los intentos de descifrado desde una IP determinada parecen llegar a pasos mayores que findtime, y por lo tanto son ignorados por fail2ban.
1519987675.92-1519986602.0es 1073.92o alrededor de 18 minutos.
Una solución a prueba de balas sería exigir el uso de TLS en la interfaz de Internet y exigir la verificación de que los certificados presentados por los clientes sean emitidos por una CA confiable.