Local System Accounts Discovery - Linux

Status: test
Severity: low
Log source: product linux, category process_creation
Author: Alejandro Ortuno, oscd.community, CheraghiMilad
Source: github.com/SigmaHQ/sigma

Detects enumeration of local system accounts. This information can help adversaries determine which local accounts exist on a system to aid in follow-on behavior.

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	`T1087.001` Account Discovery: Local Account

Event coverage

Provider	Event
Sysmon-for-Linux	Event ID 1

Rule body yaml

title: Local System Accounts Discovery - Linux
id: b45e3d6f-42c6-47d8-a478-df6bd6cf534c
status: test
description: Detects enumeration of local system accounts. This information can help adversaries determine which local accounts exist on a system to aid in follow-on behavior.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1087.001/T1087.001.md
    - https://my.f5.com/manage/s/article/K589
    - https://man.freebsd.org/cgi/man.cgi?pwd_mkdb
author: Alejandro Ortuno, oscd.community, CheraghiMilad
date: 2020-10-08
modified: 2024-12-10
tags:
    - attack.discovery
    - attack.t1087.001
logsource:
    category: process_creation
    product: linux
detection:
    selection_1:
        Image|endswith: '/lastlog'
    selection_2:
        CommandLine|contains: '''x:0:'''
    selection_3:
        Image|endswith:
            - '/cat'
            - '/ed'
            - '/head'
            - '/more'
            - '/nano'
            - '/tail'
            - '/vi'
            - '/vim'
            - '/less'
            - '/emacs'
            - '/sqlite3'
            - '/makemap'
        CommandLine|contains:
            - '/etc/passwd'
            - '/etc/shadow'
            - '/etc/sudoers'
            - '/etc/spwd.db'
            - '/etc/pwd.db'
            - '/etc/master.passwd'
    selection_4:
        Image|endswith: '/id'
    selection_5:
        Image|endswith: '/lsof'
        CommandLine|contains: '-u'
    condition: 1 of selection*
falsepositives:
    - Legitimate administration activities
level: low

Stages and Predicates

Stage 0: `condition`

1 of selection*

Stage 1: `selection_1`

selection_1:
    Image|endswith: '/lastlog'

Stage 2: `selection_2`

selection_2:
    CommandLine|contains: '''x:0:'''

Stage 3: `selection_3`

selection_3:
    Image|endswith:
        - '/cat'
        - '/ed'
        - '/head'
        - '/more'
        - '/nano'
        - '/tail'
        - '/vi'
        - '/vim'
        - '/less'
        - '/emacs'
        - '/sqlite3'
        - '/makemap'
    CommandLine|contains:
        - '/etc/passwd'
        - '/etc/shadow'
        - '/etc/sudoers'
        - '/etc/spwd.db'
        - '/etc/pwd.db'
        - '/etc/master.passwd'

Stage 4: `selection_4`

selection_4:
    Image|endswith: '/id'

Stage 5: `selection_5`

selection_5:
    Image|endswith: '/lsof'
    CommandLine|contains: '-u'

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	`'x:0:'` `-u` `/etc/master.passwd` `/etc/passwd` `/etc/pwd.db` `/etc/shadow` `/etc/spwd.db` `/etc/sudoers`
`Image`	ends_with	`/cat` `/ed` `/emacs` `/head` `/id` `/lastlog` `/less` `/lsof` `/makemap` `/more` `/nano` `/sqlite3` `/tail` `/vi` `/vim`

`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)

Local System Accounts Discovery - Linux

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_1`

Stage 2: `selection_2`

Stage 3: `selection_3`

Stage 4: `selection_4`

Stage 5: `selection_5`

Indicators

Keyboard shortcuts

Search operators

Local System Accounts Discovery - Linux

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_1

Stage 2: selection_2

Stage 3: selection_3

Stage 4: selection_4

Stage 5: selection_5

Indicators

Stage 0: `condition`

Stage 1: `selection_1`

Stage 2: `selection_2`

Stage 3: `selection_3`

Stage 4: `selection_4`

Stage 5: `selection_5`