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This homework assignment requires the knowledge from Modules 6 and 7.  
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This homework assignment requires the knowledge from Modules 6 and 7.
  
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Create SEC rules that accomplish the following event correlation task:
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=== Create SEC rules that accomplish the following event correlation task: ===
  
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1) monitor sshd log events and detect SSH probing from remote hosts, where
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1) if netfilter firewall blocked packet events have been seen for the same host repeatedly during 2 minutes, so that the host has probed at least 5 distinct TCP and/or UDP ports, memorize that host for the following 1 hour as suspicious host. Note that ports must be distinguished not only by port number, but transport protocol should also be considered (for example, ports 53/tcp and 53/udp must be regarded different).
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the same non-existing user account is probed over SSH from 3 distinct IP
 
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addresses within 60 seconds or less.
 
  
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For example, if the following events appear in the log
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For example, if the following events appear for host 192.168.56.1, this host should be memorized as suspicious, since it has probed 5 distinct ports 161/udp, 21/tcp, 23/tcp, 25/tcp, and 123/udp within 2 minutes:
  
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Nov  7 12:53:11 myhost sshd[10477]: Failed password for invalid user admin2 from 10.3.6.22 port 50087 ssh2
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Nov  7 14:14:48 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=32 TOS=0x00 PREC=0x00 TTL=64 ID=32591 DF PROTO=UDP SPT=46062 DPT=161 LEN=12  
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Nov  7 14:15:06 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=32 TOS=0x00 PREC=0x00 TTL=64 ID=34001 DF PROTO=UDP SPT=37036 DPT=161 LEN=12
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Nov  7 14:15:18 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=37323 DF PROTO=TCP SPT=38954 DPT=21 WINDOW=29200 RES=0x00 SYN URGP=0
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Nov  7 14:15:22 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=3465 DF PROTO=TCP SPT=51418 DPT=23 WINDOW=29200 RES=0x00 SYN URGP=0
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Nov  7 14:15:23 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=3466 DF PROTO=TCP SPT=51418 DPT=23 WINDOW=29200 RES=0x00 SYN URGP=0
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Nov  7 14:16:01 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=60601 DF PROTO=TCP SPT=50250 DPT=25 WINDOW=29200 RES=0x00 SYN URGP=0
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Nov  7 14:16:02 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=60602 DF PROTO=TCP SPT=50250 DPT=25 WINDOW=29200 RES=0x00 SYN URGP=0
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Nov  7 14:16:46 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=32 TOS=0x00 PREC=0x00 TTL=64 ID=39224 DF PROTO=UDP SPT=41553 DPT=123 LEN=12
  
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Nov  7 12:53:12 myhost sshd[10477]: Failed password for invalid user admin2 from 10.3.6.22 port 50087 ssh2
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2) if a host has been previously memorized as suspicious, and from this host 3 distinct non-existing user accounts are probed over SSH within 1 minute, send an alert e-mail to the local root user (root@localhost). After e-mail has been sent, disable all further alert e-mails for the same host for the following 3 hours.
  
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Nov  7 12:53:39 myhost sshd[10479]: Failed password for invalid user oracle from 10.3.6.24 port 9899 ssh2
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For example, suppose the host 192.168.56.1 has been memorized as suspicious less than 1 hour ago, and the following events are observed:
  
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Nov  7 12:53:40 myhost sshd[10479]: Failed password for invalid user oracle from 10.3.6.24 port 9899 ssh2
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Nov  7 14:36:09 localhost sshd[1336]: Failed none for invalid user admin from 192.168.56.1 port 36404 ssh2
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Nov  7 14:36:10 localhost sshd[1336]: Failed password for invalid user admin from 192.168.56.1 port 36404 ssh2
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Nov  7 14:36:16 localhost sshd[1338]: Failed password for invalid user oracle from 192.168.56.1 port 36406 ssh2
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Nov  7 14:36:50 localhost sshd[1340]: Failed none for invalid user sybase from 192.168.56.1 port 36412 ssh2
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Nov  7 14:36:53 localhost sshd[1340]: Failed password for invalid user sybase from 192.168.56.1 port 36412 ssh2
  
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Nov  7 12:54:01 myhost sshd[10527]: Failed password for invalid user admin2 from 10.1.2.52 port 40106 ssh2
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Since 3 distinct non-existing user accounts admin, oracle, and sybase have been probed over SSH from suspicious host 192.168.56.1 within 1 minute, an alert e-mail about this host must be sent to root@localhost at 14:36:50. Also, further alerting must be disabled for 192.168.56.1 for 3 hours.
  
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Nov  7 12:54:02 myhost sshd[10527]: Failed password for invalid user admin2 from 10.1.2.52 port 40106 ssh2
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Note that all parts of the solution must be '''fully functional''' even when port probing or user account probing is conducted from '''several hosts in parallel''' (for example, contexts maintained by different counting operations must '''not''' interfere with each other).
  
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Nov  7 12:54:07 myhost sshd[10543]: Failed password for invalid user admin2 from 10.17.8.9 port 32444 ssh2''
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=== Some hints for accomplishing this assignment: ===
  
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your SEC rule should detect SSH probing for non-existing use admin2, since
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* consider the technique outlined on slides 17-18 of Module 7,
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this user was probed between 12:53:11 and 12:54:07 from 3 distinct IP addresses
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* as an alternative, consider the technique described in section 6.4 of the SEC tutorial (https://simple-evcorr.github.io/SEC-tutorial.pdf),
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10.3.6.22, 10.1.2.52 and 10.17.8.9.
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* make sure you have a good understanding of the lab assignment solutions of Modules 6 and 7.
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Also note that the detection should be done with a sliding window approach --
 
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if the counting operation for some non-existing user has not seen enough events
 
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during 60 seconds, the 60 second detection window should be moved forward.
 
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2) if the previous condition has been detected for 3 distinct non-existing users
 
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during 900 seconds (for example, admin2, oracle and testuser3 have been probed
 
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within 900 seconds), report this event to the local root-user via e-mail. After
 
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an e-mail has been sent, ensure than no repeated e-mails are generated during
 
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the following 3600 seconds.
 
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Some hints for accomplishing this assignment:
 
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* don't try to solve the whole assignment with just one rule, but rather write several rules which interact,
 
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* if SSH probing for some non-existing user account is detected (as described in the first subtask), you could generate a relevant synthetic event for this user, in order to provide input for further event correlation rules.
 
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Apart from studying the examples from the course slides, have a look at the SEC
 
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man page (installed at the virtual machines or found at
 
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http://simple-evcorr.sourceforge.net/man.html).
 

Viimane redaktsioon: 13. november 2025, kell 16:27

This homework assignment requires the knowledge from Modules 6 and 7.

Create SEC rules that accomplish the following event correlation task:

1) if netfilter firewall blocked packet events have been seen for the same host repeatedly during 2 minutes, so that the host has probed at least 5 distinct TCP and/or UDP ports, memorize that host for the following 1 hour as suspicious host. Note that ports must be distinguished not only by port number, but transport protocol should also be considered (for example, ports 53/tcp and 53/udp must be regarded different).

For example, if the following events appear for host 192.168.56.1, this host should be memorized as suspicious, since it has probed 5 distinct ports 161/udp, 21/tcp, 23/tcp, 25/tcp, and 123/udp within 2 minutes: 

Nov  7 14:14:48 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=32 TOS=0x00 PREC=0x00 TTL=64 ID=32591 DF PROTO=UDP SPT=46062 DPT=161 LEN=12 
Nov  7 14:15:06 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=32 TOS=0x00 PREC=0x00 TTL=64 ID=34001 DF PROTO=UDP SPT=37036 DPT=161 LEN=12 
Nov  7 14:15:18 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=37323 DF PROTO=TCP SPT=38954 DPT=21 WINDOW=29200 RES=0x00 SYN URGP=0 
Nov  7 14:15:22 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=3465 DF PROTO=TCP SPT=51418 DPT=23 WINDOW=29200 RES=0x00 SYN URGP=0 
Nov  7 14:15:23 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=3466 DF PROTO=TCP SPT=51418 DPT=23 WINDOW=29200 RES=0x00 SYN URGP=0 
Nov  7 14:16:01 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=60601 DF PROTO=TCP SPT=50250 DPT=25 WINDOW=29200 RES=0x00 SYN URGP=0 
Nov  7 14:16:02 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=60602 DF PROTO=TCP SPT=50250 DPT=25 WINDOW=29200 RES=0x00 SYN URGP=0 
Nov  7 14:16:46 localhost kernel: iptables: IN=enp0s8 OUT= MAC=08:00:27:ce:72:9a:0a:00:27:00:00:00:08:00 SRC=192.168.56.1 DST=192.168.56.103 LEN=32 TOS=0x00 PREC=0x00 TTL=64 ID=39224 DF PROTO=UDP SPT=41553 DPT=123 LEN=12

2) if a host has been previously memorized as suspicious, and from this host 3 distinct non-existing user accounts are probed over SSH within 1 minute, send an alert e-mail to the local root user (root@localhost). After e-mail has been sent, disable all further alert e-mails for the same host for the following 3 hours.

For example, suppose the host 192.168.56.1 has been memorized as suspicious less than 1 hour ago, and the following events are observed: 

Nov  7 14:36:09 localhost sshd[1336]: Failed none for invalid user admin from 192.168.56.1 port 36404 ssh2
Nov  7 14:36:10 localhost sshd[1336]: Failed password for invalid user admin from 192.168.56.1 port 36404 ssh2
Nov  7 14:36:16 localhost sshd[1338]: Failed password for invalid user oracle from 192.168.56.1 port 36406 ssh2
Nov  7 14:36:50 localhost sshd[1340]: Failed none for invalid user sybase from 192.168.56.1 port 36412 ssh2
Nov  7 14:36:53 localhost sshd[1340]: Failed password for invalid user sybase from 192.168.56.1 port 36412 ssh2

Since 3 distinct non-existing user accounts admin, oracle, and sybase have been probed over SSH from suspicious host 192.168.56.1 within 1 minute, an alert e-mail about this host must be sent to root@localhost at 14:36:50. Also, further alerting must be disabled for 192.168.56.1 for 3 hours.

Note that all parts of the solution must be fully functional even when port probing or user account probing is conducted from several hosts in parallel (for example, contexts maintained by different counting operations must not interfere with each other).

Some hints for accomplishing this assignment:

  • consider the technique outlined on slides 17-18 of Module 7,
  • as an alternative, consider the technique described in section 6.4 of the SEC tutorial (https://simple-evcorr.github.io/SEC-tutorial.pdf),
  • make sure you have a good understanding of the lab assignment solutions of Modules 6 and 7.
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