#17: Logging and Auditing
You need to configure logging and auditing to collect all hacking and cracking attempts. By default syslog stores data in /var/log/ directory. This is also useful to find out software misconfiguration which may open your system to various attacks. See the following logging related articles:
- Linux log file locations.
- How to send logs to a remote loghost.
- How do I rotate log files?.
- man pages syslogd, syslog.conf and logrotate.
#17.1: Monitor Suspicious Log Messages With Logwatch / Logcheck
Read your logs using logwatch or logcheck. These tools make your log reading life easier. You get detailed reporting on unusual items in syslog via email. A sample syslog report:
################### Logwatch 7.3 (03/24/06) ####################
Processing Initiated: Fri Oct 30 04:02:03 2009
Date Range Processed: yesterday
( 2009-Oct-29 )
Period is day.
Detail Level of Output: 0
Type of Output: unformatted
Logfiles for Host: www-52.nixcraft.net.in
##################################################################
--------------------- Named Begin ------------------------
**Unmatched Entries**
general: info: zone XXXXXX.com/IN: Transfer started.: 3 Time(s)
general: info: zone XXXXXX.com/IN: refresh: retry limit for master ttttttttttttttttttt#53 exceeded (source ::#0): 3 Time(s)
general: info: zone XXXXXX.com/IN: Transfer started.: 4 Time(s)
general: info: zone XXXXXX.com/IN: refresh: retry limit for master ttttttttttttttttttt#53 exceeded (source ::#0): 4 Time(s)
---------------------- Named End -------------------------
--------------------- iptables firewall Begin ------------------------
Logged 87 packets on interface eth0
From 58.y.xxx.ww - 1 packet to tcp(8080)
From 59.www.zzz.yyy - 1 packet to tcp(22)
From 60.32.nnn.yyy - 2 packets to tcp(45633)
From 222.xxx.ttt.zz - 5 packets to tcp(8000,8080,8800)
---------------------- iptables firewall End -------------------------
--------------------- SSHD Begin ------------------------
Users logging in through sshd:
root:
123.xxx.ttt.zzz: 6 times
---------------------- SSHD End -------------------------
--------------------- Disk Space Begin ------------------------
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 450G 185G 241G 44% /
/dev/sda1 99M 35M 60M 37% /boot
---------------------- Disk Space End -------------------------
###################### Logwatch End #########################(Note output is truncated)
#17.2: System Accounting with auditd
The auditd is provided for system auditing. It is responsible for writing audit records to the disk. During startup, the rules in /etc/audit.rules are read by this daemon. You can open /etc/audit.rules file and make changes such as setup audit file log location and other option. With auditd you can answers the following questions:
- System startup and shutdown events (reboot / halt).
- Date and time of the event.
- User respoisble for the event (such as trying to access /path/to/topsecret.dat file).
- Type of event (edit, access, delete, write, update file & commands).
- Success or failure of the event.
- Records events that Modify date and time.
- Find out who made changes to modify the system's network settings.
- Record events that modify user/group information.
- See who made changes to a file etc.
See our quick tutorial which explains enabling and using the auditd service.
#18: Secure OpenSSH Server
The SSH protocol is recommended for remote login and remote file transfer. However, ssh is open to many attacks. See how to secure OpenSSH server:
#19: Install And Use Intrusion Detection System
A network intrusion detection system (NIDS) is an intrusion detection system that tries to detect malicious activity such as denial of service attacks, port scans or even attempts to crack into computers by monitoring network traffic.
It is a good practice to deploy any integrity checking software before system goes online in a production environment. If possible install AIDE software before the system is connected to any network. AIDE is a host-based intrusion detection system (HIDS) it can monitor and analyses the internals of a computing system.
Snort is a software for intrusion detection which is capable of performing packet logging and real-time traffic analysis on IP networks.
#20: Protecting Files, Directories and Email
Linux offers excellent protections against unauthorized data access. File permissions and MAC prevent unauthorized access from accessing data. However, permissions set by the Linux are irrelevant if an attacker has physical access to a computer and can simply move the computer's hard drive to another system to copy and analyze the sensitive data. You can easily protect files, and partitons under Linux using the following tools:
- To encrypt and decrypt files with a password, use gpg command.
- Linux or UNIX password protect files with openssl and other tools.
- See how to encrypting directories with ecryptfs.
- TrueCrypt is free open-source disk encryption software for Windows 7/Vista/XP, Mac OS X and Linux.
- Howto: Disk and partition encryption in Linux for mobile devices.
- How to setup encrypted Swap on Linux.
#20.1: Securing Email Servers
You can use SSL certificates and gpg keys to secure email communication on both server and client computers: