Persistence Via Sudoers.d Files

Status: test
Severity: medium
Log source: product linux, category file_event
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the creation or modification of files within the "sudoers.d" directory on Linux systems. Such activity may indicate an attempt to establish or maintain privilege escalation by granting specific users elevated permissions. Unauthorized changes to sudoers files are a common technique used by attackers to persist administrative access.

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1548.003` Abuse Elevation Control Mechanism: Sudo and Sudo Caching

Event coverage

Provider	Event
Sysmon-for-Linux	Event ID 11

Rule body yaml

title: Persistence Via Sudoers.d Files
id: ddb26b76-4447-4807-871f-1b035b2bfa5d
status: test
description: |
    Detects the creation or modification of files within the "sudoers.d" directory on Linux systems.
    Such activity may indicate an attempt to establish or maintain privilege escalation by granting specific users elevated permissions.
    Unauthorized changes to sudoers files are a common technique used by attackers to persist administrative access.
references:
    - https://github.com/h3xduck/TripleCross/blob/1f1c3e0958af8ad9f6ebe10ab442e75de33e91de/apps/deployer.sh
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-07-05
modified: 2026-03-18
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1548.003
logsource:
    product: linux
    category: file_event
detection:
    selection:
        TargetFilename|startswith: '/etc/sudoers.d/'
    filter_main_dpkg:
        Image|endswith: '/usr/bin/dpkg'
        TargetFilename: '/etc/sudoers.d/README.dpkg-new'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Creation of legitimate files in sudoers.d folder as part of administrator work
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    TargetFilename|startswith: '/etc/sudoers.d/'

Stage 2: `not filter_main_dpkg`

filter_main_dpkg:
    Image|endswith: '/usr/bin/dpkg'
    TargetFilename: '/etc/sudoers.d/README.dpkg-new'

Exclusions

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

Field	Kind	Excluded values
`Image`	ends_with	`/usr/bin/dpkg`
`TargetFilename`	eq	`/etc/sudoers.d/README.dpkg-new`

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
`TargetFilename`	starts_with	`/etc/sudoers.d/`

`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)

Persistence Via Sudoers.d Files

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_dpkg`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Persistence Via Sudoers.d Files

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_dpkg

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_dpkg`