How do I automatically ban UDP short packet with Fail2Ban?
The failregex needs to match the full output, and can take the form of a full regular expression, so something like so:
'^.*kernel: UDP: short packet: From <HOST>:.*$'
You can test your regular expressions by using (documentation):
fail2ban-regex -v /var/log/kern.log /etc/fail2ban/filter.d/ddos.conf
Tested and verified below:
cwatson@loki:~$ cat ./kern.log
Dec 19 16:05:12 03-serv kernel: UDP: short packet: From 74.60.6.213:1900 311/299 to x.x.x.x:27015
Dec 19 16:05:57 03-serv kernel: UDP: short packet: From 1.215.252.130:1900 11297/286 to x.x.x.x:27015
Dec 19 16:08:17 03-serv kernel: UDP: short packet: From 184.0.249.136:1900 363/299 to x.x.x.x:27015
Dec 19 16:09:54 03-serv kernel: UDP: short packet: From 1.214.66.49:1900 11297/310 to x.x.x.x:27015
Dec 19 16:11:28 03-serv kernel: UDP: short packet: From 1.214.214.2:1900 11297/320 to x.x.x.x:27015
Dec 19 18:00:45 03-serv kernel: UDP: short packet: From 74.60.171.197:1900 295/279 to x.x.x.x:27015
Dec 19 18:00:59 03-serv kernel: UDP: short packet: From 112.155.240.24:1900 11297/300 to x.x.x.x:27015
Dec 20 16:02:07 03-serv kernel: UDP: short packet: From 1.220.200.162:1900 11297/312 to x.x.x.x:27015
Dec 20 16:02:30 03-serv kernel: UDP: short packet: From 1.215.123.171:1900 11297/302 to x.x.x.x:27015
cwatson@loki:~$ fail2ban-regex -v ./kern.log "^.*kernel: UDP: short packet: From <HOST>:.*$"
Running tests
=============
Use failregex line : ^.*kernel: UDP: short packet: From <HOST>:.*$
Use log file : ./kern.log
Results
=======
Failregex: 9 total
|- #) [# of hits] regular expression
| 1) [9] ^.*kernel: UDP: short packet: From <HOST>:.*$
| 74.60.6.213 Fri Dec 19 16:05:12 2014
| 1.215.252.130 Fri Dec 19 16:05:57 2014
| 184.0.249.136 Fri Dec 19 16:08:17 2014
| 1.214.66.49 Fri Dec 19 16:09:54 2014
| 1.214.214.2 Fri Dec 19 16:11:28 2014
| 74.60.171.197 Fri Dec 19 18:00:45 2014
| 112.155.240.24 Fri Dec 19 18:00:59 2014
| 1.220.200.162 Sat Dec 20 16:02:07 2014
| 1.215.123.171 Sat Dec 20 16:02:30 2014
`-
Ignoreregex: 0 total
Date template hits:
|- [# of hits] date format
| [9] MONTH Day Hour:Minute:Second
| [0] WEEKDAY MONTH Day Hour:Minute:Second[.subsecond] Year
| [0] WEEKDAY MONTH Day Hour:Minute:Second Year
| [0] WEEKDAY MONTH Day Hour:Minute:Second
| [0] Year/Month/Day Hour:Minute:Second
| [0] Day/Month/Year Hour:Minute:Second
| [0] Day/Month/Year2 Hour:Minute:Second
| [0] Day/MONTH/Year:Hour:Minute:Second
| [0] Month/Day/Year:Hour:Minute:Second
| [0] Year-Month-Day Hour:Minute:Second[,subsecond]
| [0] Year-Month-Day Hour:Minute:Second
| [0] Year.Month.Day Hour:Minute:Second
| [0] Day-MONTH-Year Hour:Minute:Second[.Millisecond]
| [0] Day-Month-Year Hour:Minute:Second
| [0] Month-Day-Year Hour:Minute:Second[.Millisecond]
| [0] TAI64N
| [0] Epoch
| [0] ISO 8601
| [0] Hour:Minute:Second
| [0] <Month/Day/Year@Hour:Minute:Second>
| [0] YearMonthDay Hour:Minute:Second
| [0] Month-Day-Year Hour:Minute:Second
`-
Lines: 9 lines, 0 ignored, 9 matched, 0 missed