Privilege abuse

This use case shows how Wazuh can audit access to sensitive data in users' home directories. We use an audit rule that monitors all files and subdirectories in a user's home directory and tracks when another user tries to access them. Then, we create a Wazuh custom rule to alert for such behavior so that security teams can take action accordingly.

Ubuntu endpoint

In this use case, we have two users, John and Jane. We monitor Jane’s home directory and track if any other user that is not Jane or root tries to access this directory.

  1. Create the two users, Jane and John, on your endpoint:

    # useradd jane
    # useradd john
  2. Edit the audit rule file /etc/audit/audit.rules and add the following configuration:

    # echo "-a always,exit -S open -S openat -F dir=/home/jane/ -F perm=rwa -F auid>=1000 -F auid!=-1 -F euid!=<EUID_OF_JANE> -F uid!=0 -C auid!=obj_uid -F key=power_abuse">>/etc/audit/audit.rules

    Here is a breakdown of the rule:

    • -a always,exit specifies that the rule should always trigger on a process exit.

    • -F dir=/home/jane/ specifies that the rule should only apply to files and directories inside the /home/jane directory.

    • -F perm=rwa specifies the permissions being monitored for the system call to occur, in this case, read, write, and append permissions.

    • -F auid>=1000 this specifies the audit UID (auid), which is the user ID associated with the process that triggered the event, should be more than or equal to 1000.

    • -F auid!=-1 specifies the auid should not be equal to -1, which is used when a process is launched without a user ID.

    • -F euid!=<EUID_OF_JANE> specifies that the audit rule should not apply to Jane herself. <EUID_OF_JANE> represents Jane’s euid. You can obtain a user euid using the following command: id -u <USERNAME>.

    • -F uid!=0 specifies that the audit rule doesn’t apply to the root user.

    • -C auid!=obj_uid specifies that the auid should not be equal to the object UID (obj_uid), which is the UID associated with the accessed file or directory.

    • -k power_abuse provides a unique ID that Wazuh uses to analyze the audit logs.

    This audit rule logs all attempts by another user to open files or directories inside Jane’s home directory.

  3. Reload the rules and confirm they are in place:

    # auditctl -R /etc/audit/rules.d/audit.rules
    # auditctl -l
    -a always,exit -S open,openat -F dir=/home/jane/ -F perm=rwa -F auid>=1000 -F auid!=-1 -F euid!=1003 -F uid!=0 -C auid!=obj_uid -F key=power_abuse

Wazuh server

  1. Update the /var/ossec/etc/lists/audit-keys CDB list with the custom audit key:

    # echo "power_abuse:abuse" >> /var/ossec/etc/lists/audit-keys
  2. Add the following rule to the custom /var/ossec/etc/rules/local_rules.xml file:

    <group name="audit">
      <rule id="100210" level="8">
        <list field="audit.key" lookup="match_key_value" check_value="abuse">etc/lists/audit-keys</list>
        <description>Audit: User with uid $(audit.uid) trying to access $( files.</description>
  3. Restart the Wazuh manager to apply the changes:

    # systemctl restart wazuh-manager

Test the configuration

Perform the following actions on the monitored endpoint to test the configuration.

  1. Switch to the user John:

    $ su john
  2. Then, try to list the content of /home/jane or open any file under this directory:

    $ ls /home/jane/

You can visualize the alerts for in the Wazuh dashboard.

Test the configuration