Binfmt Configuration File Creation
ELASTIC detection rule by Elastic · Elastic License v2
This rule detects the creation of a binfmt configuration file. Binfmt is a utility that is used to
configure the behavior of the Linux kernel when executing binary files. By creating a malicious
binfmt configuration file, threat actors can execute a backdoor script or command on the target system.
[metadata]
creation_date = "2026/08/25"
integration = ["endpoint"]
maturity = "production"
updated_date = "2026/08/31"
[rule]
author = ["Elastic"]
description = """
This rule detects the creation of a binfmt configuration file. Binfmt is a utility that is used to
configure the behavior of the Linux kernel when executing binary files. By creating a malicious
binfmt configuration file, threat actors can execute a backdoor script or command on the target system.
"""
from = "now-9m"
index = ["logs-endpoint.events.file*"]
language = "eql"
license = "Elastic License v2"
name = "Binfmt Configuration File Creation"
note = """ ## Triage and analysis
> **Disclaimer**:
> This investigation guide was created using generative AI technology and has been reviewed to improve its accuracy and relevance. While every effort has been made to ensure its quality, we recommend validating the content and adapting it to suit your specific environment and operational needs.
### Investigating Binfmt Configuration File Creation
This rule detects creation of Linux binfmt configuration files or registrations that alter how the kernel handles executable formats, which may establish persistent command execution. An attacker can register a crafted binary signature and interpreter so that launching a matching executable automatically invokes a backdoor script under the initiating user’s privileges.
### Possible investigation steps
- Inspect the new configuration or registration content for unusual magic bytes, masks, flags, extensions, and interpreter paths that reference scripts, writable directories, temporary locations, or network-mounted files.
- Review the creating process’s user, command line, parent chain, working directory, package provenance, and nearby shell or privilege-escalation activity to determine whether the change was authorized.
- Correlate the event with systemd-binfmt restarts, writes to the binfmt_misc register interface, and subsequent execution of the configured interpreter or matching binaries.
- Search across the environment for the same configuration content, interpreter path, file hash, or responsible account to identify additional affected hosts and determine campaign scope.
- If unauthorized, preserve the configuration and relevant telemetry, disable or unregister the handler, remove persistence artifacts, and investigate the originating account and process for further compromise.
### False positive analysis
- An administrator or approved automation may create a binfmt configuration to support a legitimate binary format, which analysts can verify by reviewing the change record, responsible account, configuration contents, and interpreter path.
- An authorized package installation or system update may register or replace a binfmt handler, which analysts can confirm by correlating the event with package activity and validating the creating process and file against expected system changes.
### Response and remediation
- Isolate the affected Linux host from untrusted networks while preserving approved management access, volatile evidence, and copies of the malicious binfmt configuration and interpreter.
- Unregister the malicious handler under `/proc/sys/fs/binfmt_misc`, remove its files from binfmt configuration directories, delete associated backdoor scripts or binaries, and restart `systemd-binfmt` only after validating remaining entries.
- Escalate immediately to incident response if the configured interpreter executed, root privileges were involved, credentials may have been exposed, or matching artifacts appear on additional hosts.
- Revoke attacker-controlled sessions, rotate credentials used on the host, and search for related scheduled tasks, services, startup files, modified SSH keys, and payloads created by the responsible process.
- Reimage the system from a known-good baseline when integrity cannot be established; otherwise restore trusted configuration files and packages, verify kernel and system binaries, and confirm only approved binfmt handlers remain.
- Restrict write access to binfmt configuration paths and registration interfaces, enforce least privilege for administrative automation, and monitor future handler creation, registration, and interpreter execution.
"""
references = ["https://dfir.ch/posts/today_i_learned_binfmt_misc/"]
risk_score = 21
rule_id = "a3b47d21-20d6-45b0-8b75-fc27073bdef2"
setup = """## 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](https://www.elastic.co/guide/en/fleet/current/fleet-server.html).
#### 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](https://www.elastic.co/guide/en/security/current/configure-endpoint-integration-policy.html).
- 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](https://www.elastic.co/guide/en/fleet/8.10/agent-policy.html).
- 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](https://www.elastic.co/guide/en/security/current/install-endpoint.html).
"""
severity = "low"
tags = [
"Domain: Endpoint",
"OS: Linux",
"Platform: Linux",
"Use Case: Threat Detection",
"Tactic: Persistence",
"Data Source: Elastic Defend",
"Resources: Investigation Guide",
]
timestamp_override = "event.ingested"
type = "eql"
query = '''
file where host.os.type == "linux" and event.action != "deletion" and process.executable != null and
file.path like (
"/etc/binfmt.d/*.conf", "/run/binfmt.d/*.conf", "/usr/local/lib/binfmt.d/*.conf", "/usr/lib/binfmt.d/*.conf",
"/proc/sys/fs/binfmt_misc/register", "/proc/sys/fs/binfmt_misc/*"
) and
not (
file.path like (
"/usr/lib/binfmt.d/python3.*.conf", "/usr/lib/binfmt.d/qemu-*-static.conf",
"/proc/sys/fs/binfmt_misc/status"
) or
process.executable == "/usr/lib/systemd/systemd-binfmt"
)
'''
[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1546"
name = "Event Triggered Execution"
reference = "https://attack.mitre.org/techniques/T1546/"
[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"