Auditd Module

The auditd module receives audit events from the Linux Audit Framework that is a part of the Linux kernel.

This module is available only for Linux.

How it works

This module establishes a subscription to the kernel to receive the events as they occur. So unlike most other modules, the period configuration option is unused because it is not implemented using polling.

The Linux Audit Framework can send multiple messages for a single auditable event. For example, a rename syscall causes the kernel to send eight separate messages. Each message describes a different aspect of the activity that is occurring (the syscall itself, file paths, current working directory, process title). This module will combine all of the data from each of the messages into a single event.

Messages for one event can be interleaved with messages from another event. This module will buffer the messages in order to combine related messages into a single event even if they arrive interleaved or out of order.

Useful commands

When running Auditbeat with the auditd module enabled, you might find that other monitoring tools interfere with Auditbeat.

For example, you might encounter errors if another process, such as auditd, is registered to receive data from the Linux Audit Framework. You can use these commands to see if the auditd service is running and stop it:

  • See if auditd is running:

    service auditd status
  • Stop the auditd service:

    service auditd stop
  • Disable auditd from starting on boot:

    chkconfig auditd off

To save CPU usage and disk space, you can use this command to stop journald from listening to audit messages:

systemctl mask systemd-journald-audit.socket

Inspect the kernel audit system status

Auditbeat provides useful commands to query the state of the audit system in the Linux kernel.

  • See the list of installed audit rules:

    auditbeat show auditd-rules

    Prints the list of loaded rules, similar to auditctl -l:

    -a never,exit -S all -F pid=26253
    -a always,exit -F arch=b32 -S all -F key=32bit-abi
    -a always,exit -F arch=b64 -S execve,execveat -F key=exec
    -a always,exit -F arch=b64 -S connect,accept,bind -F key=external-access
    -w /etc/group -p wa -k identity
    -w /etc/passwd -p wa -k identity
    -w /etc/gshadow -p wa -k identity
    -a always,exit -F arch=b64 -S open,truncate,ftruncate,creat,openat,open_by_handle_at -F exit=-EACCES -F key=access
    -a always,exit -F arch=b64 -S open,truncate,ftruncate,creat,openat,open_by_handle_at -F exit=-EPERM -F key=access
  • See the status of the audit system:

    auditbeat show auditd-status

    Prints the status of the kernel audit system, similar to auditctl -s:

    enabled 1
    failure 0
    pid 0
    rate_limit 0
    backlog_limit 8192
    lost 14407
    backlog 0
    backlog_wait_time 0
    features 0xf

Configuration options

This module has some configuration options for tuning its behavior. The following example shows all configuration options with their default values.

- module: auditd
  resolve_ids: true
  failure_mode: silent
  backlog_limit: 8192
  rate_limit: 0
  include_raw_message: false
  include_warnings: false
  backpressure_strategy: auto
socket_type

This optional setting controls the type of socket that Auditbeat uses to receive events from the kernel. The two options are unicast and multicast.

unicast should be used when Auditbeat is the primary userspace daemon for receiving audit events and managing the rules. Only a single process can receive audit events through the "unicast" connection so any other daemons should be stopped (e.g. stop auditd).

multicast can be used in kernel versions 3.16 and newer. By using multicast Auditbeat will receive an audit event broadcast that is not exclusive to a a single process. This is ideal for situations where auditd is running and managing the rules. If multicast is specified, but the kernel version is less than 3.16 Auditbeat will automatically revert to unicast.

By default Auditbeat will use multicast if the kernel version is 3.16 or newer and no rules have been defined. Otherwise unicast will be used.

resolve_ids
This boolean setting enables the resolution of UIDs and GIDs to their associated names. The default value is true.
failure_mode
This determines the kernel’s behavior on critical failures such as errors sending events to Auditbeat, the backlog limit was exceeded, the kernel ran out of memory, or the rate limit was exceeded. The options are silent, log, or panic. silent basically makes the kernel ignore the errors, log makes the kernel write the audit messages using printk so they show up in system’s syslog, and panic causes the kernel to panic to prevent use of the machine. Auditbeat’s default is silent.
backlog_limit
This controls the maximum number of audit messages that will be buffered by the kernel.
rate_limit
This sets a rate limit on the number of messages/sec delivered by the kernel. The default is 0, which disables rate limiting. Changing this value to anything other than zero can cause messages to be lost. The preferred approach to reduce the messaging rate is be more selective in the audit ruleset.
include_raw_message
This boolean setting causes Auditbeat to include each of the raw messages that contributed to the event in the document as a field called messages. The default value is false. This setting is primarily used for development and debugging purposes.
include_warnings
This boolean setting causes Auditbeat to include as warnings any issues that were encountered while parsing the raw messages. The default value is false. When this setting is enabled the raw messages will be included in the event regardless of the include_raw_message config setting. This setting is primarily used for development and debugging purposes.
audit_rules
A string containing the audit rules that should be installed to the kernel. There should be one rule per line. Comments can be embedded in the string using # as a prefix. The format for rules is the same used by the Linux auditctl utility. Auditbeat supports adding file watches (-w) and syscall rules (-a or -A).
audit_rule_files
A list of files to load audit rules from. This files are loaded after the rules declared in audit_rules are loaded. Wildcards are supported and will expand in lexicographical order. The format is the same as that of the audit_rules field.
backpressure_strategy

Specifies the strategy that Auditbeat uses to prevent backpressure from propagating to the kernel and impacting audited processes.

The possible values are:

  • auto (default): Auditbeat uses the kernel strategy, if supported, or falls back to the userspace strategy.
  • kernel: Auditbeat sets the backlog_wait_time in the kernel’s audit framework to 0. This causes events to be discarded in the kernel if the audit backlog queue fills to capacity. Requires a 3.14 kernel or newer.
  • userspace: Auditbeat drops events when there is backpressure from the publishing pipeline. If no rate_limit is set, Auditbeat sets a rate limit of 5000. Users should test their setup and adjust the rate_limit option accordingly.
  • both: Auditbeat uses the kernel and userspace strategies at the same time.
  • none: No backpressure mitigation measures are enabled.

Audit rules

The audit rules are where you configure the activities that are audited. These rules are configured as either syscalls or files that should be monitored. For example you can track all connect syscalls or file system writes to /etc/passwd.

Auditing a large number of syscalls can place a heavy load on the system so consider carefully the rules you define and try to apply filters in the rules themselves to be as selective as possible.

The kernel evaluates the rules in the order in which they were defined so place the most active rules first in order to speed up evaluation.

You can assign keys to each rule for better identification of the rule that triggered an event and easier filtering later in Elasticsearch.

Defining any audit rules in the config causes Auditbeat to purge all existing audit rules prior to adding the rules specified in the config. Therefore it is unnecessary and unsupported to include a -D (delete all) rule.

auditbeat.modules:
- module: auditd
  audit_rules: |
    # Things that affect identity.
    -w /etc/group -p wa -k identity
    -w /etc/passwd -p wa -k identity
    -w /etc/gshadow -p wa -k identity
    -w /etc/shadow -p wa -k identity

    # Unauthorized access attempts to files (unsuccessful).
    -a always,exit -F arch=b32 -S open,creat,truncate,ftruncate,openat,open_by_handle_at -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -F key=access
    -a always,exit -F arch=b32 -S open,creat,truncate,ftruncate,openat,open_by_handle_at -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -F key=access
    -a always,exit -F arch=b64 -S open,truncate,ftruncate,creat,openat,open_by_handle_at -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -F key=access
    -a always,exit -F arch=b64 -S open,truncate,ftruncate,creat,openat,open_by_handle_at -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -F key=access

Example configuration

The Auditd module supports the common configuration options that are described under configuring Auditbeat. Here is an example configuration:

auditbeat.modules:
- module: auditd
  # Load audit rules from separate files. Same format as audit.rules(7).
  audit_rule_files: [ '${path.config}/audit.rules.d/*.conf' ]
  audit_rules: |
    ## Define audit rules here.
    ## Create file watches (-w) or syscall audits (-a or -A). Uncomment these
    ## examples or add your own rules.

    ## If you are on a 64 bit platform, everything should be running
    ## in 64 bit mode. This rule will detect any use of the 32 bit syscalls
    ## because this might be a sign of someone exploiting a hole in the 32
    ## bit API.
    #-a always,exit -F arch=b32 -S all -F key=32bit-abi

    ## Executions.
    #-a always,exit -F arch=b64 -S execve,execveat -k exec

    ## External access (warning: these can be expensive to audit).
    #-a always,exit -F arch=b64 -S accept,bind,connect -F key=external-access

    ## Identity changes.
    #-w /etc/group -p wa -k identity
    #-w /etc/passwd -p wa -k identity
    #-w /etc/gshadow -p wa -k identity

    ## Unauthorized access attempts.
    #-a always,exit -F arch=b64 -S open,creat,truncate,ftruncate,openat,open_by_handle_at -F exit=-EACCES -k access
    #-a always,exit -F arch=b64 -S open,creat,truncate,ftruncate,openat,open_by_handle_at -F exit=-EPERM -k access