Chmod Targeting Sensitive Directories

Status: test
Severity: medium
Log source: product linux, category process_creation
Author: Christopher Peacock @SecurePeacock, SCYTHE @scythe_io
Source: github.com/SigmaHQ/sigma

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.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	`T1222.002` File and Directory Permissions Modification: Linux and Mac Permissions

Event coverage

Provider	Event
Sysmon-for-Linux	Event ID 1

Rule body yaml

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

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    Image|endswith: '/chmod'
    CommandLine|contains:
        - '/tmp/'
        - '/.Library/'
        - '/etc/'
        - '/opt/'

Stage 2: `not filter_main_*`

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'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`CommandLine`	match	`/etc/`
`ParentCommandLine`	match	`.postinst configure`
`ParentCommandLine`	match	`/var/lib/dpkg/info/`
`CommandLine`	match	`chmod --reference=/etc/shells`
`ParentCommandLine`	ends_with	`/update-shells`
`CommandLine`	eq	`chmod 0775 /etc/landscape/`
`CommandLine`	eq	`chmod 644 /etc/apparmor.d/tunables/home.d/ubuntu`
`CommandLine`	starts_with	`chmod 700 /tmp/apt-key-gpghome.`
`CommandLine`	starts_with	`chmod 755 /var/tmp/mkinitramfs`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`/.Library/` `/etc/` `/opt/` `/tmp/`
`Image`	ends_with	`/chmod`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Chmod Targeting Sensitive Directories

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Chmod Targeting Sensitive Directories

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`