Booby Trapping Samba Shares
This is a simple guide to setting up fake Samba shares that’ll send you an email when accessed. The idea is that an attacker, after getting into your network, is going to search around for the good stuff. If you mix in low hanging fruit, it can give you an early indicator if someone is in your network.
This guide is assuming you already have a configured Samba server, up and operational.
Unfortunately, I couldn’t find any way to separate out log files based on share. What we’ll need to do is make sure auditing is configured, and look through syslogs for anything suspicious.
A note about auditing
Fair warning, depending on your normal usage, this will create a lot of log entries. The settings below will log pretty much everything your users do on the server. As someone who has dealt with “Well, I don’t know what happened, my work just disappeared” a few too many times, I think it is a very fair price to pay.
Extra settings for [global]
The following extra settings need to be enabled in the [global] section of your smb.conf:
full_audit:prefix = %u|%I|%S
full_audit:failure = connect
full_audit:success = connect disconnect mkdir rmdir open close read pread write pwrite sendfile rename unlink chmod fchmod chown fchown chdir ftruncate lock symlink readlink link mknod realpath
full_audit:facility = local5
full_audit:priority = notice
vfs object = full_audit
This enables full auditing, and has it log to syslog. If necessary, you can always scale it back by changing what gets actually logged. The one we definitely use is chdir for the rule below.
Next, create the share (or shares) that you want to be traps. A simple example is below:
[passwords] comment = Centralized Password Storage path = /srv/samba/passwords
Create the folder and give it read permissions.
user@server:~/$ sudo mkdir -p /srv/samba/passwords user@server:~/$ sudo chmod a+rX /srv/samba/passwords
Restart samba, and all the audit data should be going to syslog.
Swatch is used for actually monitoring the log file, to look for a specific pattern, and take action when it finds a result. First things first, we’ll install swatch. It is a pretty standard application, and should be available in the package manager of your choice. For example, also in Ubuntu:
user@server:~/$ sudo apt-get install swatch
Next, create a config file. Here is a very simple one:
user@server:~$ cat /etc/swatch.conf watchfor /passwords\|chdir\|ok\|chdir/ echo mail = email@example.com
Change out ‘passwords’ with whatever you have named your share. The text inside the /data/ is what will be matched by swatch. You can add other strings to catch on here if you want, but this will notify you the first time a user accesses a share.
NOTE: FOR THE LOVE OF GOD, MAKE SURE YOU PUT THAT BACKSLASH IN FRONT OF THAT PIPE. Pipe by itself means OR, which means you’ll match a lot of things. Your coworkers will not be happy with 1000s of alerts within a few minutes.
Next, you’ll need to set up the init.d/systemd startup script. Below is a sample of each:
user@server:~/$ sudo chmod +x /etc/init.d/swatch user@server:~/$ sudo update-rc.d swatch defaults user@server:~/$ sudo service swatch start
/usr/lib/systemd/system/swatch.service [Unit] Description=Swatch Log Monitoring Daemon After=syslog.target [Service] ExecStart=/usr/bin/swatch --config-file=/etc/swatch.conf --tail-file=/var/log/syslog --pid-file=/var/run/swatch.pid --daemon ExecStop=kill -s KILL $(cat /var/run/swatch.pid) Type=forking PIDFile=/var/run/swatch/pid [Install] WantedBy=multi-user.target user@server:~/$ sudo systemctl enable swatch.service user@server:~/$ sudo systemctl start swatch.service
Now that you have your nice booby-trapped Samba share, you can always take it a step further and put some fun items in.