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fail2ban não detecta ataque de força bruta de senha SMTP

tag-icon • tag-icon debian security postfix fail2ban sasl
fail2ban não detecta ataque de força bruta de senha SMTP

Spammers estão executando ataques de força bruta para adivinhação de senha em meu servidor (postfix no Debian). Eles já adivinharam as senhas de dois usuários e começaram a enviar spam usando meu servidor. Senhas alteradas e ataques atenuados (por enquanto), mas quero bloqueá-los completamente.

Instalei o fail2ban, mas por algum motivo ele não consegue detectar os ataques.

/etc/fail2ban/fail.confcontém:

[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.confcontém:

# 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 =

Quando executo o filtro /var/log/mail.warn, ele produz 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.

Apesar de tudo isso, /var/log/fail2ban.lognão mostra bloqueio do endereço IP infrator.

Atualizar

Seguindo sugestões, aumentei o nível do log. Isso mostra:

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

O jail.conf tem:

bantime  = 600
maxretry = 3

Responder1

Do Ignore line since time 1519986602.0 < 1519987675.92 - 600registro de log eos documentos, presumo que esse 600seja o valor da findtimeopção. Ou seja, as tentativas de crack de um determinado IP parecem ocorrer em passos maiores que findtimee, portanto, são ignoradas por fail2ban.

1519987675.92-1519986602.0é 1073.92ou cerca de 18 minutos.

Uma solução à prova de balas seria exigir o uso de TLS na interface voltada para a Internet e exigir a verificação de que os certificados apresentados pelos clientes são emitidos por uma CA confiável.

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