Chmod Targeting Sensitive Directories

SIGMA detection rule by Christopher Peacock @SecurePeacock, SCYTHE @scythe_io · NOASSERTION

Detects chmod targeting files in sensitive directory paths on Linux systems. Attackers may use chmod to change permissions of files in these directories to maintain persistence, escalate privileges, or disrupt system operations.

title: Chmod Targeting Sensitive Directories
id: 6419afd1-3742-47a5-a7e6-b50386cd15f8
status: test
description: |
    Detects chmod targeting files in sensitive directory paths on Linux systems.
    Attackers may use chmod to change permissions of files in these directories to maintain persistence, escalate privileges, or disrupt system operations.
references:
    - https://www.intezer.com/blog/malware-analysis/new-backdoor-sysjoker/
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1222.002/T1222.002.md
author: 'Christopher Peacock @SecurePeacock, SCYTHE @scythe_io'
date: 2022-06-03
modified: 2026-03-18
tags:
    - attack.defense-impairment
    - attack.t1222.002
logsource:
    product: linux
    category: process_creation
detection:
    selection:
        Image|endswith: '/chmod'
        CommandLine|contains:
            - '/tmp/'
            - '/.Library/'
            - '/etc/'
            - '/opt/'
    filter_main_update_shells:
        CommandLine|contains: 'chmod --reference=/etc/shells'
        ParentCommandLine|endswith: '/update-shells'
    filter_main_postinst:
        CommandLine|contains: '/etc/'
        ParentCommandLine|contains|all:
            - '/var/lib/dpkg/info/'
            - '.postinst configure'
    filter_main_apt_key:
        CommandLine|startswith: 'chmod 700 /tmp/apt-key-gpghome.'
    filter_main_mkinitramfs:
        CommandLine|startswith: 'chmod 755 /var/tmp/mkinitramfs'
    filter_main_landscape:
        CommandLine: 'chmod 0775 /etc/landscape/'
    filter_main_ubuntu_apparmor:
        CommandLine: 'chmod 644 /etc/apparmor.d/tunables/home.d/ubuntu'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Some false positives are to be expected. Apply additional filters as needed before pushing to production.
level: medium

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90c42731-ab96-4df7-8fd2-e9167916504c

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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