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Audit Logs

1. Install Auditd:

Auditd is the user space component to the Linux Auditing System. It allows you to track system calls and create detailed logs about system activities.

sudo apt-get update
sudo apt-get install auditd

2. Enable and Start Auditd:

After installation, start and enable the auditd service.

sudo systemctl start auditd
sudo systemctl enable auditd

3. Auditd Persistence:

Some Linux distributions have a mechanism to manage audit rules that persist across reboots. Instead of directly editing the audit.rules file, use the auditctl command to add and manage rules.

To add a rule, use the auditctl command. For example:

sudo auditctl -w /var/run/utmp -p wa -k logins

This will add the rule to the active rule set.

4. Auditd Service Restart:

If you've been manually editing the audit.rules file, remember to restart the auditd service after making changes to ensure the new rules take effect:

sudo systemctl restart auditd

5. View Audit Logs:

Audit logs are stored in /var/log/audit/audit.log. You can use ausearch or other tools to query and analyze the logs.

To view all audit logs related to logins:

ausearch -i -k logins

The -i option in the command provides additional information about the events.

Shows audit events related to rule modifications made using auditctl. This output indicates that audit rules were added, changed, and removed. Each entry provides information about the type of event, the action performed, and relevant details.

Audit logs are stored in the /var/log/audit/audit.log file by default. You can view the audit log by directly examining this file:

sudo less /var/log/audit/audit.log

Audit Rules:

To configure audit rules in Ubuntu using the /etc/audit/audit.rules file and the /etc/audit/rules.d/ directory, you can follow these steps:

  1. Understanding Rule Groups:

The /etc/audit/audit.rules file and the /etc/audit/rules.d/ directory are used to define different sets of audit rules. These rules specify what events to monitor and log. The numbers preceding the rule filenames indicate the priority and grouping of the rules.

  • 10: Kernel and auditctl configuration
  • 20: Rules that could match general rules but you want a different match
  • 30: Main rules
  • 40: Optional rules
  • 50: Server-specific rules
  • 70: System local rules
  • 90: Finalize (immutable)
  1. Configuring Audit Rules:

Here are some example rules for each of the rule groups:

  1. 10: Kernel and auditctl configuration:

These rules are typically used to configure global audit settings and set up initial monitoring.

• Enable auditd startup at boot:

# /etc/audit/rules.d/10-configuration.rules
-e 2

• Set auditd backlog limit:

# /etc/audit/rules.d/10-configuration.rules
-b 8192
  1. 20: Rules that could match general rules but you want a different match:

These rules are used when you want specific rules to take precedence over more general rules.

• Log failed login attempts (preferably using a system-specific rule):

# /etc/audit/rules.d/20-specific-login.rules
-a always,exit -F arch=b64 -S sethostname -F success=0 -k login-failure
  1. 30: Main rules:

These rules capture the core events you want to monitor. Note that these examples are basic; you might want to expand them based on your needs.

• Monitor file read and write actions:

# /etc/audit/rules.d/30-file-access.rules
-a always,exit -F arch=b64 -S open,creat,truncate,ftruncate,openat,open_by_handle_at -k file-access

• Monitor changes to system administration files:

# /etc/audit/rules.d/30-admin-files.rules
-a always,exit -F arch=b64 -S chmod,chown,chgrp,fchmod,fchown,fchownat -k admin-file-change
  1. 40: Optional rules:

These rules can include additional events you consider important to monitor, but not critical.

• Monitor changes to network configuration:

# /etc/audit/rules.d/40-network.rules
-a always,exit -F arch=b64 -S sethostname,setdomainname -k network-change
  1. 50: Server-specific rules:

These rules can be tailored to your server's specific requirements and services.

• Monitor changes to web server configuration files:

# /etc/audit/rules.d/50-web-server.rules
-a always,exit -F arch=b64 -S chmod,chown,chgrp,fchmod,fchown,fchownat -F path=/etc/nginx/* -k web-config-change
  1. 70: System local rules:

These rules focus on local system actions that might be relevant to your environment.

• Monitor changes to user and group information:

# /etc/audit/rules.d/70-user-group.rules
-a always,exit -F arch=b64 -S useradd,usermod,userdel,groupadd,groupmod,groupdel -k user-group-change
  1. 90: Finalize (immutable):

These rules are meant to enforce immutability on the audit configuration itself.

• Lock the audit configuration to prevent changes:

# /etc/audit/rules.d/90-finalize.rules
-e 2
-a always,exit -F arch=b64 -S auditctl -F success=0 -k audit-config-change

Remember that these are just examples, and you should tailor them to your environment's specific requirements. After adding or modifying rules, always reload the audit rules using sudo service auditd reload for the changes to take effect. Additionally, monitor the audit logs to ensure that the configured rules are capturing the desired events.

[OPTIONAL]

Log Rotation:

Audit logs can grow large over time. By default, most Linux distributions are configured to rotate and retain audit logs automatically. If not set, consider setting up log rotation to manage the log file size:

sudo nano /etc/audit/auditd.conf

Find and update the max_log_file parameter:

max_log_file = <size in MB>

Then restart the auditd service.

sudo systemctl restart auditd

  1. Log Rotation: When the audit log file (audit.log) reaches a certain size, it is rotated. Log rotation involves renaming the current log file to audit.log.1 and creating a new audit.log file to continue logging events.

  2. Retention Policy: The /etc/audit/auditd.conf file includes settings related to log retention. Specifically, the max_log_file and num_logs options determine how many log files are retained and their maximum size. For example, if max_log_file is set to 50 MB and num_logs is set to 5, the audit system will retain up to 5 log files, each of which can be up to 50 MB in size. Older log files are deleted automatically when new ones are created.

  3. Log Compression: Older log files that are rotated may be compressed to save disk space. Compressed log files have extensions like .gz (e.g., audit.log.1.gz). The compression helps reduce storage space usage.

If you need to change the default log retention settings, you can modify the /etc/audit/auditd.conf file to adjust the max_log_file and num_logs values to suit your needs. After making changes, you may need to restart the auditd service for the new settings to take effect.

You can check if the audit rules are applied to the system in Ubuntu using the auditctl command.

Use the auditctl -l command to list the currently loaded audit rules. This will show you the active rules:

sudo auditctl -l

If you want to check if a specific rule is loaded, you can use grep to search for it in the output. For example:

sudo auditctl -l | grep "10-configuration.rules"

This will check if the 10-configuration.rules rule is loaded.

If you have created an audit rule file, but the rules are not showing up when you run sudo auditctl -l, it's possible that the rules have not been applied or loaded into the audit subsystem.

To load all the audit rules from /etc/audit/rules.d/, you can use the auditctl command. Here's how you can do it:

auditctl -R /etc/audit/rules.d/

To see the any particular rule loaded or not, you can use the -R option with auditctl

auditctl -R /etc/audit/rules.d/10-configuration.rules

This command will load the rules from the specified file, but it won't make them active immediately. To activate the rules, you can either restart the auditd service or use auditctl with the -e option.

To activate the rules immediately, you can use:

auditctl -e 1

This sets the audit daemon into enabled mode (1), which will activate the loaded rules.

After activating the rules, you can check if they are active by running:

auditctl -l

Shell History

To check the shell history of a particular user on an Ubuntu system, you can examine the user's shell history file.

1. Viewing the History File:

The shell history is stored in the user's home directory in a file named .bash_history for the Bash shell.

cat /home/<username>/.bash_history

2. Searching the history

You can use the grep command to search for specific commands within the user's shell history. This can be helpful when you're looking for a specific command or pattern.

grep "search_string" /home/<username>/.bash_history

Replace "search_string" with the command or keyword you're looking for.

3. View Command History with Timestamps:

Open a terminal and use the following commands to view the command history of the user along with date and time information:

HISTTIMEFORMAT="%Y-%m-%d %T"
history

This command sets the HISTTIMEFORMAT variable to the desired timestamp format (Year-Month-Day Hour:Minute:Second) and then displays the command history with timestamps.

[Optional] To set date and time format to command history, open your Bash configuration file in a text editor. This is typically ~/.bashrc for individual users or /etc/bash.bashrc for system-wide configuration. Use the appropriate file based on your needs:

For the current user:

nano ~/.bashrc

For the system-wide configuration (requires root privileges):

sudo nano /etc/bash.bashrc

Add the following lines at the end of the file to set the HISTTIMEFORMAT environment variable:

# Set the timestamp format for command history
export HISTTIMEFORMAT="%F %T "

This configuration sets the timestamp format to "YYYY-MM-DD HH:MM:SS".

Save the file and exit the text editor.

To apply the changes to your current session, either close and reopen your terminal or run:

source ~/.bashrc   # For individual user configuration

or

source /etc/bash.bashrc   # For system-wide configuration

Now, when you view your shell history using the history command, it will display each command with the timestamp of when it was executed.

4. Searching the History:

You can use the grep command along with the HISTTIMEFORMAT setting to search for specific commands or patterns within the history:

HISTTIMEFORMAT="%Y-%m-%d %T"
history | grep "search_string"

Replace "search_string" with the command or keyword you're looking for.

Authentication Logs

These logs record login attempts and other authentication-related information, including the IP addresses or sources of the connections. On Ubuntu systems, the authentication logs are stored in the /var/log/auth.log file.

1. View the Authentication Logs:

Open the /var/log/auth.log file using a text editor or a command-line tool. You will need superuser privileges to view this file.

sudo less /var/log/auth.log

2. Search for the User and Command:

Within the auth.log file, you can search for the user's name and the command you're interested in. Use a tool like grep to narrow down the results. Replace <username> with the actual username of the non-root user and <command> with the command executed.

sudo grep "<username>" /var/log/auth.log | grep "<command>"

This command will display the authentication logs related to the specified user and command. Look for entries that indicate successful logins or executed commands.

3. Check IP Addresses or Sources:

In the search results, you will see entries with IP addresses or sources from which the user logged in. These entries typically include the IP address or hostname in the from field.

For Example:

Aug 30 10:00:00 hostname sshd[12345]: Accepted password for <username> from <source_IP> port <source_port> ssh2

In this example, <source_IP> and <source_port> indicate the IP address and port from which the user logged in.

Please note that the auth.log file contains a variety of authentication-related events, including SSH logins, sudo command executions, and more. You'll need to review the relevant entries to find the information you're looking for.