File Integrity Monitoring

Applies to Product: USM Appliance™ AlienVault OSSIM®

You can configure AlienVault HIDS to perform File Integrity Monitoring (FIM), which identifies changes in system files, folders, and Microsoft Windows registries. The process that identifies these changes is syscheck. The syscheck process scans the host at user-defined intervals and stores checksums of watched files. The system then generates an event when a checksum changes.

In addition to using syscheck, you can also configure Windows systems so that AlienVault HIDS agents forward object access audit events for USM Appliance to process. These events provide more information on operations affecting file and folder objects, such as who performed specific actions or operations on an object. For more information, see Configuring Windows Systems to View Windows Audit Object Access Events.

Configuring File Integrity Monitoring

Every HIDS agent includes an ossec.conf file with some default settings for syscheck. On Microsoft Windows hosts, you can find this file in C:\Program Files (x86)\ossec-agent, and on Linux, in /var/ossec/etc.

When you make changes through the USM Appliance web interface, USM Appliance records your modifications in the agent.conf file and stores it for distribution. When the agent authenticates, it will download the shared configuration and merge it with the local copy. The shared file will take precedence, overwriting any local configuration.

Default settings for the ossec.conf file stored on a host system are configured when the HIDS agent is first installed or deployed on a host system. In addition, an ossec.conf file containing syscheck and other global options is defined and stored on theUSM Appliance Server. For more information on viewing and configuring this file, see To configureUSM Appliance server-side (global) ossec.conf settings.

To change syscheck options for all agents

  1. Go to Environment > Detection.

  2. On HIDS, click Agents, and then click Syschecks.

  3. Configure the options according to your needs.

  4. Click Save after making changes in each section.
  5. (Optional) Click Agent.conf to confirm the changes in XML format.
  6. To apply your changes immediately, click HIDS Control, and then Restart .

To configureUSM Appliance server-side (global) ossec.conf settings

  1. Go to Environment > Detection.

  2. On HIDS, click Config, and then click Syschecks.

  3. Configure the options according to your needs.

  4. You can also view the contents of the server ossec.conf file in XML format by selecting the Config >Configuration option.

The following table describes syscheck options that you can specify through the USM Appliance web interface.

Syscheck options

Options

Meanings

Default Values

Frequency

Frequency at which the syscheck executes (in seconds).

72000s (20h)

Scan_day

Day of the week to run the scans.

None

Alert New Files

Whether to alert on new files created. (Global agent option; not configurable for individual hosts.)

No

Scan Time

Time to start the scans.

None

Auto Ignore

Whether to ignore files that change too often. (Global agent option; not configurable for individual hosts.)

No

Scan on Start

Whether to do the first scan as soon as the agent starts.

Yes

Windows Registry Entries Monitored

Microsoft Windows registries to monitor.

See the ossec.conf file on a Windows host

Registry Entries Ignored

Microsoft Windows registries not to monitor.

See the ossec.conf file on a Windows host

Files/Directories Monitored

Files or directories to monitor.

See the ossec.conf file on a Windows host

 

Realtime

Real time or continuous monitoring on Linux (using the inotify system calls) and Windows systems.

No

 

Report Changes

(Linux‑like systems only) Whether to report file changes. Limited to text files.

No

 

Chk All

Checks all changes listed below.

No

 

Chk Sum

Check the md5 and sha1 hashes of the files.

No

 

Chk Sha1sum

Check the sha1 hashes of the files.

No

 

Chk Size

Checks the size of the files.

No

 

Chk Owner

Checks the owner of the files.

No

 

Chk Group

Checks the group owner of the files/directories.

No

 

Chk Perm

Checks the permission of the files/directories.

No

File/Directories Ignored

Files or directories not to monitor.

See the ossec.conf file on a Windows host

About Auto Ignore and Realtime

With Auto Ignore set to No, you receive alerts on every file change, regardless how many times it is changed. If you also select the Realtime option, the alert stops after the third change, equivalent to setting Auto Ignore to Yes.

About Alert New Files

You can configure AlienVault HIDS to alert on new files, but it does not report in real time, because AlienVault HIDS can only detect new files on a full scan.

To enable alerting on new files

  1. Change Alert New Files to Yes.
  2. Specify the directory in which to detect the new files.
  3. Select Chk All.

About Report Changes

The report_changes option is only available on UNIX-like systems. Setting this option globally, or reporting on changes to the root file system, will likely create a large number of events, which could potentially fill up all available disk space and impact USM Appliance operation.

Specifying Different Syscheck Options for Different Hosts

You can configure different syscheck options for different hosts, by entering them in the agent.conf file manually. Ensure that you

  • Use a separate <agent_config> element for each host you need to configure.
  • Use the name attribute to denote the name of the host. (This is the agent name used when adding the agent to the detection section.)
  • Specify the options you want to change inside the <syscheck> element.
  • Repeat all every host you want to configure.

The following example shows different syscheck options for host AD2012 and Win2008:

<agent_config name="AD2012">

<syscheck>

<frequency>21600</frequency>

<scan_on_start>yes</scan_on_start>

<directories check_all="yes">C:\temp</directories>

</syscheck>

</agent_config>

 

<agent_config name="Win2008">

<syscheck>

<frequency>3600</frequency>

<scan_on_start>yes</scan_on_start>

<directories check_all="yes">C:\topsecret</directories>

</syscheck>

</agent_config>

Instead of making these changes on the hosts one-by-one, you can configure them in the USM Appliance web interface.

To configure different syscheck options for different hosts

  1. Go to Environment > Detection.

  2. On HIDS, click Agents > Agent.conf.

    By default, this page is blank.

  3. Type or paste in the changes you want to make.
  4. Click Save.

  5. (Optional) Click Syscheck. Notice that a list appears towards the upper-right corner with the name of the first entry in agent.conf.

    Agent.conf page for configuring syscheck options.

  6. To apply your changes immediately, click HIDS Control, and then Restart.

Viewing the File Integrity Monitoring Events

Each time an AlienVault HIDS agent detects a change in a monitored file or directory, USM Appliance creates an event and stores it in the database.

To view FIM events

  1. Go to Analysis > Security Events (SIEM).
  2. In Data Sources, select "AlienVault HIDS".
  3. In Event Name, type "Integrity".

  4. Click Go.

    SIEM page that displays file integrity monitoring events.

  5. View event details to determine which file has changed.

    Event Details section from Security Events (SIEM).

Configuring Windows Systems to View Windows Audit Object Access Events

To configure Windows systems so that AlienVault USM Appliance can view Windows audit object access events, you need to first edit local security policy settings. After applying policy changes to include audit object events in Windows security logs, the AlienVault HIDS agent will forward those events to USM Appliance.

Note: You can only set up file and folder auditing on NTFS drives.

To define policy settings for object access audit events

  1. On a selected Windows system, open the Local Group Policy Editor.

  2. Go to Computer Configuration > Windows Settings > Security Settings > Local Policies > Audit Policy.

  3. Edit the Audit object access policy and enable auditing of Success and Failure attempts.

    The following display shows an example:

    Windows system configuration - set audit policy to enable collection of object access audit events

To apply or modify auditing policy settings

  1. Open Windows Explorer and navigate to the file or folder you want to audit.

  2. Right-click on the file or folder and select Properties.

  3. Select the Security tab and click Advanced.

  4. Select the Auditing tab and click Continue if prompted.

  5. Perform one of the following operations:

    • To set up auditing for a new user or group, click Add. In the Enter the object name to select field, type the name of the user or group that you want to audit, then click OK.
    • To remove auditing for an existing group or user, highlight the group or user name, click Remove, and then click OK. You can skip remaining steps.
    • To view or change auditing for an existing group or user, click its name and then click Edit.

  6. In the Apply onto box, click the location that you want to audit.

  7. In the Access box, indicate what actions you want to audit by selecting the appropriate check boxes.
  8. If you want to prevent subordinate files and subfolders of the original object from inheriting audit settings, select the Apply these auditing entries to objects and/or containers within this container only check box.

    9. Note: Because the Windows security log is limited in size, select the files and folders to be audited carefully, since new audit events will be stored there. Also, consider the amount of disk space that you want to devote to the security log. The maximum size for the security log is set in Event Viewer.

    After enabling object access auditing, you can view the security log in Event Viewer to see that the audit events are now collected. The AlienVault HIDS agent will forward those events to USM Appliance.