Detection: Linux Possible Bootloader Modification

Updated Date: 2026-07-08 ID: 97fd4330-bd47-4742-abaf-c877d404822a Author: Raven Tait, Nasreddine Bencherchali, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects processes modifying data in the EFI volume on Linux. These files are responsible for initializing the Boot Manager during system startup. Modification or replacement of these files is highly unusual in normal operations and may indicate an attempt to install a bootkit, persist malicious code at the firmware level, or otherwise tamper with the system boot process.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6from datamodel=Endpoint.Processes where
 7
 8(
 9    Processes.process_name IN (
10        "cp",
11        "mv",
12        "ln"
13    )
14    Processes.process_current_directory="*/EFI/BOOT*"
15)
16OR
17(
18    Processes.process="*/EFI/BOOT*"
19    NOT Processes.process_name IN (
20        "ls",
21        "grep",
22        "egrep"
23    )
24)
25
26by Processes.process Processes.vendor_product Processes.user_id
27   Processes.process_hash Processes.parent_process_name Processes.parent_process_exec
28   Processes.action Processes.dest Processes.process_current_directory Processes.process_path
29   Processes.process_integrity_level Processes.original_file_name Processes.parent_process
30   Processes.parent_process_path Processes.parent_process_guid Processes.parent_process_id
31   Processes.process_guid Processes.process_id Processes.user Processes.process_name
32
33
34| `drop_dm_object_name(Processes)`
35
36| `security_content_ctime(firstTime)`
37
38| `security_content_ctime(lastTime)`
39
40| `linux_possible_bootloader_modification_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 1	Linux	`'sysmon:linux'`	`'Syslog:Linux-Sysmon/Operational'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
linux_possible_bootloader_modification_filter	`search *`

linux_possible_bootloader_modification_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1542.001	System Firmware	Persistence

Exploitation

Installation

DE.CM

CIS 10

CVE

CVE-2024-7344

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Finding (Notable)	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Intermediate Finding (Risk Event)	Yes

TTP detections generate a Finding (Notable) and may generate Intermediate Findings (Risk Events) for associated entities.

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Legitimate system administrators or package managers such as grub or shim may modify EFI volume files during OS upgrades or bootloader updates. Filter based on known update processes or trusted administrative activity.

Associated Analytic Story

Finding

Title	Entity Field	Entity Type	Risk Score
Possible bootloader modification identified via [$process$] by [$user$] on [$dest$]	dest	system	50

Intermediate Findings

Message	Entity Field	Entity Type	Risk Score
Possible bootloader modification via [$process$] by [$user$] on [$dest$].	user	user	50

Threat Objects

Field	Type
process	process
process_name	process_name
parent_process_name	parent_process_name

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`Syslog:Linux-Sysmon/Operational`	`sysmon:linux`
Integration	✅ Passing	Dataset	`Syslog:Linux-Sysmon/Operational`	`sysmon:linux`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub |

Version: 1