Password Policy Discovery - Linux

Status: stable
Severity: low
Log source: product linux, service auditd
Author: Ömer Günal, oscd.community, Pawel Mazur
Source: github.com/SigmaHQ/sigma

Detects password policy discovery commands

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	`T1201` Password Policy Discovery

Event coverage

Provider	Event
Linux-Auditd	Event ID 1302
Linux-Auditd	Event ID 1309

Rule body yaml

title: Password Policy Discovery - Linux
id: ca94a6db-8106-4737-9ed2-3e3bb826af0a
status: stable
description: Detects password policy discovery commands
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1201/T1201.md
    - https://linux.die.net/man/1/chage
    - https://man7.org/linux/man-pages/man1/passwd.1.html
    - https://superuser.com/questions/150675/how-to-display-password-policy-information-for-a-user-ubuntu
author: Ömer Günal, oscd.community, Pawel Mazur
date: 2020-10-08
modified: 2024-12-01
tags:
    - attack.discovery
    - attack.t1201
logsource:
    product: linux
    service: auditd
detection:
    selection_files:
        type: 'PATH'
        name:
            - '/etc/login.defs'
            - '/etc/pam.d/auth'
            - '/etc/pam.d/common-account'
            - '/etc/pam.d/common-auth'
            - '/etc/pam.d/common-password'
            - '/etc/pam.d/system-auth'
            - '/etc/security/pwquality.conf'
    selection_chage:
        type: 'EXECVE'
        a0: 'chage'
        a1:
            - '--list'
            - '-l'
    selection_passwd:
        type: 'EXECVE'
        a0: 'passwd'
        a1:
            - '-S'
            - '--status'
    condition: 1 of selection_*
falsepositives:
    - Legitimate administration activities
level: low

Stages and Predicates

Stage 0: `condition`

1 of selection_*

Stage 1: `selection_files`

selection_files:
    type: 'PATH'
    name:
        - '/etc/login.defs'
        - '/etc/pam.d/auth'
        - '/etc/pam.d/common-account'
        - '/etc/pam.d/common-auth'
        - '/etc/pam.d/common-password'
        - '/etc/pam.d/system-auth'
        - '/etc/security/pwquality.conf'

Stage 2: `selection_chage`

selection_chage:
    type: 'EXECVE'
    a0: 'chage'
    a1:
        - '--list'
        - '-l'

Stage 3: `selection_passwd`

selection_passwd:
    type: 'EXECVE'
    a0: 'passwd'
    a1:
        - '-S'
        - '--status'

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
`a0`	eq	`chage` `passwd`
`a1`	eq	`--list` `--status` `-S` `-l`
`name`	eq	`/etc/login.defs` `/etc/pam.d/auth` `/etc/pam.d/common-account` `/etc/pam.d/common-auth` `/etc/pam.d/common-password` `/etc/pam.d/system-auth` `/etc/security/pwquality.conf`
`type`	eq	`EXECVE` `PATH`

`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)

Password Policy Discovery - Linux

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_files`

Stage 2: `selection_chage`

Stage 3: `selection_passwd`

Indicators

Keyboard shortcuts

Search operators

Password Policy Discovery - Linux

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_files

Stage 2: selection_chage

Stage 3: selection_passwd

Indicators

Stage 0: `condition`

Stage 1: `selection_files`

Stage 2: `selection_chage`

Stage 3: `selection_passwd`