垃圾邮件发送者正在对我的服务器（Debian 上的 postfix）进行暴力密码猜测攻击。他们已经猜出了两个用户的密码并开始使用我的服务器发送垃圾邮件。密码已更改，攻击已减轻（目前），但我想完全阻止他们。
我安装了 fail2ban，但由于某种原因它无法检测到攻击。
/etc/fail2ban/fail.conf包含：
[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.conf包含：
# 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 =
当我运行过滤器时/var/log/mail.warn，它产生结果：
# 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.
尽管如此，/var/log/fail2ban.log并没有显示阻止有问题的 IP 地址。
更新
根据建议，我提高了日志级别。这显示：
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
jail.conf 包含：
bantime = 600
maxretry = 3
答案1
从Ignore line since time 1519986602.0 < 1519987675.92 - 600日志记录和文档，我猜想这600是选项的值findtime。也就是说，来自给定 IP 的破解尝试似乎比 更大findtime，因此被 忽略fail2ban。
1519987675.92-1519986602.0是1073.92或者大约18分钟。
一个万无一失的解决方案是强制在面向 Internet 的界面上使用 TLS，并强制验证客户端提供的证书是否由受信任的 CA 颁发。