Wlrmdr.EXE Uncommon Argument Or Child Process

Status: experimental
Severity: medium
Log source: product windows, category process_creation
Author: frack113, manasmbellani
Source: github.com/SigmaHQ/sigma

Detects the execution of "Wlrmdr.exe" with the "-u" command line flag which allows anything passed to it to be an argument of the ShellExecute API, which would allow an attacker to execute arbitrary binaries. This detection also focuses on any uncommon child processes spawned from "Wlrmdr.exe" as a supplement for those that posses "ParentImage" telemetry.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Wlrmdr.EXE Uncommon Argument Or Child Process
id: 9cfc00b6-bfb7-49ce-9781-ef78503154bb
status: experimental
description: |
    Detects the execution of "Wlrmdr.exe" with the "-u" command line flag which allows anything passed to it to be an argument of the ShellExecute API, which would allow an attacker to execute arbitrary binaries.
    This detection also focuses on any uncommon child processes spawned from "Wlrmdr.exe" as a supplement for those that posses "ParentImage" telemetry.
references:
    - https://twitter.com/0gtweet/status/1493963591745220608?s=20&t=xUg9DsZhJy1q9bPTUWgeIQ
    - https://lolbas-project.github.io/lolbas/Binaries/Wlrmdr/
author: frack113, manasmbellani
date: 2022-02-16
modified: 2025-10-31
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent: # This selection is looking for processes spawned from wlrmdr using the "-u" flag
        ParentImage|endswith: '\wlrmdr.exe'
    selection_child_img:
        - Image|endswith: '\wlrmdr.exe'
        - OriginalFileName: 'WLRMNDR.EXE'
    selection_child_cli_flags_s:
        CommandLine|contains|windash: '-s '
    selection_child_cli_flags_f:
        CommandLine|contains|windash: '-f '
    selection_child_cli_flags_t:
        CommandLine|contains|windash: '-t '
    selection_child_cli_flags_m:
        CommandLine|contains|windash: '-m '
    selection_child_cli_flags_a:
        CommandLine|contains|windash: '-a '
    selection_child_cli_flags_u:
        CommandLine|contains|windash: '-u '
    filter_main_winlogon:
        ParentImage: 'C:\Windows\System32\winlogon.exe'
    filter_main_empty:
        ParentImage:
            - ''
            - '-'
    filter_main_null:
        ParentImage: null
    condition: selection_parent or (all of selection_child_* and not 1 of filter_main_*)
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection_parent or (all of selection_child_* and not 1 of filter_main_*)

Stage 1: `selection_parent`

selection_parent:
    ParentImage|endswith: '\wlrmdr.exe'

Stage 2: `selection_child_img`

selection_child_img:
    - Image|endswith: '\wlrmdr.exe'
    - OriginalFileName: 'WLRMNDR.EXE'

Stage 3: `selection_child_cli_flags_s`

selection_child_cli_flags_s:
    CommandLine|contains|windash: '-s '

Stage 4: `selection_child_cli_flags_f`

selection_child_cli_flags_f:
    CommandLine|contains|windash: '-f '

Stage 5: `selection_child_cli_flags_t`

selection_child_cli_flags_t:
    CommandLine|contains|windash: '-t '

Stage 6: `selection_child_cli_flags_m`

selection_child_cli_flags_m:
    CommandLine|contains|windash: '-m '

Stage 7: `selection_child_cli_flags_a`

selection_child_cli_flags_a:
    CommandLine|contains|windash: '-a '

Stage 8: `selection_child_cli_flags_u`

selection_child_cli_flags_u:
    CommandLine|contains|windash: '-u '

Stage 9: `not filter_main_*`

filter_main_winlogon:
    ParentImage: 'C:\Windows\System32\winlogon.exe'
filter_main_empty:
    ParentImage:
        - ''
        - '-'
filter_main_null:
    ParentImage: null

Exclusions

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

Field	Kind	Excluded values
`ParentImage`	eq	`-`
`ParentImage`	eq	`C:\Windows\System32\winlogon.exe`
`ParentImage`	is_null	(no value, null check)

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	`-a` transforms: `windash` corpus 3 (sigma 3) `-f` transforms: `windash` corpus 2 (sigma 1, splunk 1) `-m` transforms: `windash` corpus 4 (sigma 4) `-s` transforms: `windash` corpus 6 (sigma 6) `-t` transforms: `windash` corpus 2 (sigma 2) `-u` transforms: `windash` corpus 5 (sigma 4, splunk 1)
`Image`	ends_with	`\wlrmdr.exe`
`OriginalFileName`	eq	`WLRMNDR.EXE`
`ParentImage`	ends_with	`\wlrmdr.exe`

`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)

Wlrmdr.EXE Uncommon Argument Or Child Process

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_parent`

Stage 2: `selection_child_img`

Stage 3: `selection_child_cli_flags_s`

Stage 4: `selection_child_cli_flags_f`

Stage 5: `selection_child_cli_flags_t`

Stage 6: `selection_child_cli_flags_m`

Stage 7: `selection_child_cli_flags_a`

Stage 8: `selection_child_cli_flags_u`

Stage 9: `not filter_main_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Wlrmdr.EXE Uncommon Argument Or Child Process

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_parent

Stage 2: selection_child_img

Stage 3: selection_child_cli_flags_s

Stage 4: selection_child_cli_flags_f

Stage 5: selection_child_cli_flags_t

Stage 6: selection_child_cli_flags_m

Stage 7: selection_child_cli_flags_a

Stage 8: selection_child_cli_flags_u

Stage 9: not filter_main_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_parent`

Stage 2: `selection_child_img`

Stage 3: `selection_child_cli_flags_s`

Stage 4: `selection_child_cli_flags_f`

Stage 5: `selection_child_cli_flags_t`

Stage 6: `selection_child_cli_flags_m`

Stage 7: `selection_child_cli_flags_a`

Stage 8: `selection_child_cli_flags_u`

Stage 9: `not filter_main_*`