NAME

laurel(8) – transform, enrich Linux audit logs

SYNOPSIS

laurel is an auditd(8) plug-in that parses Linux audit events, enriches them with local information, and transforms them into a JSONlines-based output format intended for consumption by log processing and SIEM software.

OPTIONS

-c FILE, --config=FILE

path to configuration file (default: unset)

-d, --dry-run

Only parse configuration and exit

-h, --help

Print short help text and exit

-v, --version

Print version and exit

DESCRIPTION

laurel is typically configured to be spawned by auditd(8) itself or by audispd(8) (for 2.x auditd versions). All audit events are fed to laurel via its standard input channel.

Sample configuration file /etc/audit/plugins.d/laurel.conf:

active = yes
direction = out
type = always
format = string
path = /usr/sbin/laurel
args = --config /etc/laurel/config.toml

An alternative setup consists of an AF_UNIX socket to which auditd(8) writes events. A connection is then established by laurel (see input setting below). In this case, the operator is responsible for starting and restarting laurel.

Example configuration file:

active = yes
direction = out
path = builtin_af_unix
type = builtin
args = 0600 /var/run/laurel.sock
format = string

CONFIGURATION

Configuration of laurel itself is done through a single configuration file in TOML format.

main section

This section contains basic operation parameters.

• user: laurel is started as root by auditd, but it drops to a dedicated user as soon as possible. Default: unset
• directory: The base directory into which all files are written. Default: . (current directory)
• statusreport-period: How often stats are written to Syslog, in seconds. Default: unset
• input: laurel can consume audit events from standard input or connect to a listening socket specified as unix:/path/to/socket at start. Defaulkt: stdin
• marker: A string that is written to the log on startup and whenever laurel writes a status report. Default: none

[auditlog] section

This section describes the main audit log file. laurel performs its own log file rotation, just like auditd(8).

• file: Filename for the audit log file. Default: audit.log
• size: Size in bytes after which the log file is rotated. Default: 10MiB
• generations: Number of generations to keep after rotation. Default: 5
• read-users: List of users that are granted read access to the log file using POSIX ACLs. Default: empty
• line-prefix: A string that is prepended to every line. Default: unset

[filterlog] section

This section describes the log file for filtered-out log events (see below). The file, size, generations, read-users, line-prefix configuration items work just like for the audit log.

[transform] section

• execve-argv: The list of EXECVE.a* fields are transformed to an ARGV list or ARGV_STR string. Set to array, string (or both). Default: array
• execve-argv-limit-bytes: Arguments are cut out of the middle long argument lists in EXECVE.ARGV or EXECVE.ARGV_STR so that this limit is not exceeded. Default: unset

[translate] section

Options that can be configured here correspond to what auditd(8) does when configured with log_format=ENRICHED.

• userdb: Add translations for uid and gid fields. Default: false
• universal: Add translations for everything else: SYSCALL.arch, SYSCALL.syscall, SOCKADDR.saddr
• drop-raw: Drop raw (numeric) syscall, arch, UID, GID values if they are translated. Default: false

[enrich] section

Options that can be configured here actually add information to events

• execve-env: A list of environment variables to dump for exec events. Default: ["LD_PRELOAD", "LD_LIBRARY_PATH"]
• container: Add container information for processes running within container runtimes. Default: true
• pid: Add context information for process IDs. Default: true
• script: If an exec syscall spawns a script (as opposed to a binary), add a SCRIPT entry to the SYSCALL record. A script is assumed if the first PATH entry does not correspond to file mentioned in SYSCALL.exe. Default: true
• user-groups: Add groups that the user (“uid”) is a member of. Default: true

[label-process] section

Labels can be attached to processes and are added to any event associated with those processes. These labels can be propagated from parent to child processes.

• label-exe.<regexp> = <label-name>: Regular expressions/label mappings applied to binary executables (SYSCALL.exe) on exec calls. Default: none
• label-script.<regexp> = <label-name>: Regular expressions/label mappings applied to scripts (SYSCALL.SCRIPT, see enrich.script description above) on exec calls. Default: none
• label-keys: A list of keys that are applied as a process label, see auditctl(8)’s -k option. Default: none
• unlabel-exe.<regexp> = <label-name>: Like label-exe, but for removing labels
• unlabel-script.<regexp> = <label-name>: Like label-script, but for removing labels
• propagate-labels: List of labels that are propagated to child processes. Default: empty

[filter] section

Filters make laurel drop entire events from the log file while still using them for internal processing such as process tracking.

• filter-keys: A list of strings that are matched against SYSCALL.key to drop the event. Default: empty
• filter-null-keys: Filter events without specified key. Default: false
• filter-labels: A list of strings that are matched against process labels. Default: empty
• filter-raw-lines: A list of regular expression that are matched against individual input lines as written by auditd(8). Events that contain such lines are then filtered. Default: empty
• filter-action: What to do with filtered events? drop or log to the filterlog defined above.
• keep-first-per-process: Keep the first event observed for any given process even if it would be filtered otherwise. This should only be turned off if reproducible process tracking or process tree reconstruction is not required. Default: true

SIGNALS

SIGHUP causes laurel to process any buffered input and restart. It can be used to reconfigure laurel without having restarting auditd(8) which would likely lead to lost audit messages.

AUTHORS

• Hilko Bengen «bengen@hilluzination.de»
• Sergej Schmidt «sergej@msgpeek.net»