Detecting privilege escalation, incident response and mitigation, Splunk

 For example, your sensitive file is configured in such a way to splunk so that any change's on that file would let you know. 

You now know your /etc/passwd file has been changed and the user did this her/her uid is 1002 and the user user /bin/cp exe tool to do this. 

From the victim server, auditd and sshd logs are forwarded to splunk. Our task is find out the user's name. 

Query in splunk:

source="/var/log/victim-server/audit.log" uid=1002 /Home

Now we shall know the username of uid 1002 which is victor.

Now this user victor may try to ssh on the victim-server. We want to know the ip address of the system from where victor trying for ssh. 

source="/var/log/victim-server/sshd.log" "failed password for victor"

now we shall get the ip address of victor's machine. 

Now there is another way to get the username of uid 1002, for that you need to what does acct auid field means in auditd logs. acct for accounts and auid for audit uid. 

source="/var/log/victim-server/audit.log" auid=1002 AND acct=* AND exe="*sshd" | top 0 acct

or 

source="/var/log/victim-server/audit.log" auid=1002 AND acct=* AND | top acct

Now investigating the audit logs, how to find what tool attacker download over https after getting access on the system?

source="/var/log/victim-server/audit.log" https   (we could also use .com keyword)

 

Now say attacker switch the user account using su command. How you gonna find that?

source="/var/log/victim-server/audit.log" uid="1002" exe="/bin/su" | top 0 acct

or

source="/var/log/victim-server/audit.log" uid="1002" exe="/bin/su"

Now we shall get the name of user account that had been switched to. 

Now access the server to investigate further:

after accessing the server issue sudo -i command to get root access. 

now type history command or cat /root/.bash_history command to see what commands previously launched by the attacker. 

check /root/.ssh/authorized_keys files. 

In this case the vulnerability lies in /bin/cp utility. Because SUID permission is set on /bin/cp utility. When this permission is set then command execute in root privileges and any unprivileged user can write to any file on the system if they use cp tool. 

so to find that tool, 

find / -perm -u=s -type f 2>/dev/null

after find that tool, now issue the below command. 

chmod u-s /bin/cp

Now remove scanner user from the /etc/passwd file. You can use vim or nano or mousepad or pluma tool to do that or can use the below command. 

sed -i "$ d" /etc/passwd

Also remove the entry from /root/.ssh/authorized_keys file. 

sed -i "$ d" /root/.ssh/authorized_keys

Avi