GRUB Configuration File Creation

This rule detects the creation of GRUB configuration files on Linux systems. The GRUB configuration file is used to configure the boot loader, which is responsible for loading the operating system. Attackers may create malicious GRUB configuration files to execute arbitrary code or escalate privileges during the boot process, which can be leveraged to maintain persistence on the system.

Rule type: eql

Rule indices:

logs-endpoint.events.file*
logs-sentinel_one_cloud_funnel.*
endgame-*

Severity: low

Risk score: 21

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

Domain: Endpoint
OS: Linux
Use Case: Threat Detection
Tactic: Persistence
Tactic: Execution
Tactic: Defense Evasion
Data Source: Elastic Defend
Data Source: SentinelOne
Data Source: Elastic Endgame

Version: 1

Rule authors:

Elastic

Rule license: Elastic License v2

Setup

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Setup

This rule requires data coming in from Elastic Defend.

Elastic Defend Integration Setup

Elastic Defend is integrated into the Elastic Agent using Fleet. Upon configuration, the integration allows the Elastic Agent to monitor events on your host and send data to the Elastic Security app.

Prerequisite Requirements:

Fleet is required for Elastic Defend.
To configure Fleet Server refer to the documentation.

The following steps should be executed in order to add the Elastic Defend integration on a Linux System:

Go to the Kibana home page and click "Add integrations".
In the query bar, search for "Elastic Defend" and select the integration to see more details about it.
Click "Add Elastic Defend".
Configure the integration name and optionally add a description.
Select the type of environment you want to protect, either "Traditional Endpoints" or "Cloud Workloads".
Select a configuration preset. Each preset comes with different default settings for Elastic Agent, you can further customize these later by configuring the Elastic Defend integration policy. Helper guide.
We suggest selecting "Complete EDR (Endpoint Detection and Response)" as a configuration setting, that provides "All events; all preventions"
Enter a name for the agent policy in "New agent policy name". If other agent policies already exist, you can click the "Existing hosts" tab and select an existing policy instead. For more details on Elastic Agent configuration settings, refer to the helper guide.
Click "Save and Continue".
To complete the integration, select "Add Elastic Agent to your hosts" and continue to the next section to install the Elastic Agent on your hosts. For more details on Elastic Defend refer to the helper guide.

Rule query

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file where host.os.type == "linux" and event.type == "creation" and process.executable != null and file.path like~ (
  "/etc/default/grub.d/*", "/etc/default/grub", "/etc/grub.d/*",
  "/boot/grub2/grub.cfg", "/boot/grub/grub.cfg", "/boot/efi/EFI/*/grub.cfg",
  "/etc/sysconfig/grub"
) and not (
  process.executable in (
    "/bin/dpkg", "/usr/bin/dpkg", "/bin/dockerd", "/usr/bin/dockerd", "/usr/sbin/dockerd", "/bin/microdnf",
    "/usr/bin/microdnf", "/bin/rpm", "/usr/bin/rpm", "/bin/snapd", "/usr/bin/snapd", "/bin/yum", "/usr/bin/yum",
    "/bin/dnf", "/usr/bin/dnf", "/bin/podman", "/usr/bin/podman", "/bin/dnf-automatic", "/usr/bin/dnf-automatic",
    "/bin/pacman", "/usr/bin/pacman", "/usr/bin/dpkg-divert", "/bin/dpkg-divert", "/sbin/apk", "/usr/sbin/apk",
    "/usr/local/sbin/apk", "/usr/bin/apt", "/usr/sbin/pacman", "/bin/podman", "/usr/bin/podman", "/usr/bin/puppet",
    "/bin/puppet", "/opt/puppetlabs/puppet/bin/puppet", "/usr/bin/chef-client", "/bin/chef-client",
    "/bin/autossl_check", "/usr/bin/autossl_check", "/proc/self/exe", "/dev/fd/*",  "/usr/bin/pamac-daemon",
    "/bin/pamac-daemon", "/usr/lib/snapd/snapd", "/usr/local/bin/dockerd", "/usr/bin/crio", "/usr/sbin/crond",
    "/opt/puppetlabs/puppet/bin/ruby", "/usr/libexec/platform-python", "/kaniko/kaniko-executor",
    "/usr/local/bin/dockerd", "/usr/bin/podman", "/bin/install", "/proc/self/exe", "/usr/lib/systemd/systemd",
    "/usr/sbin/sshd", "/usr/bin/gitlab-runner", "/opt/gitlab/embedded/bin/ruby", "/usr/sbin/gdm", "/usr/bin/install",
    "/usr/local/manageengine/uems_agent/bin/dcregister", "/usr/local/bin/pacman"
  ) or
  process.executable like~ (
    "/nix/store/*", "/var/lib/dpkg/*", "/tmp/vmis.*", "/snap/*", "/dev/fd/*", "/usr/lib/virtualbox/*"
  ) or
  file.extension in ("swp", "swpx", "swx", "dpkg-remove") or
  (process.name == "sed" and file.name : "sed*")
)

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Persistence
- ID: TA0003
- Reference URL: https://attack.mitre.org/tactics/TA0003/
Technique:
- Name: Pre-OS Boot
- ID: T1542
- Reference URL: https://attack.mitre.org/techniques/T1542/
Technique:
- Name: Create or Modify System Process
- ID: T1543
- Reference URL: https://attack.mitre.org/techniques/T1543/
Technique:
- Name: Hijack Execution Flow
- ID: T1574
- Reference URL: https://attack.mitre.org/techniques/T1574/

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