Suspicious Space Characters in RunMRU Registry Path - ClickFix

Status: experimental
Severity: high
Log source: product windows, category registry_set
Author: Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the occurrence of numerous space characters in RunMRU registry paths, which may indicate execution via phishing lures using clickfix techniques to hide malicious commands in the Windows Run dialog box from naked eyes.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1204.004` User Execution: Malicious Copy and Paste
Stealth	`T1027.010` Obfuscated Files or Information: Command Obfuscation

Event coverage

Provider	Event	Title
Sysmon	Event ID 13	RegistryEvent (Value Set)

Rule body yaml

title: Suspicious Space Characters in RunMRU Registry Path - ClickFix
id: 7a1b4c5e-8f3d-4b9a-7c2e-1f4a5b8c6d9e
related:
    - id: 3ae9974a-eb09-4044-8e70-8980a50c12c8
      type: similar
status: experimental
description: |
    Detects the occurrence of numerous space characters in RunMRU registry paths, which may indicate execution via phishing lures using clickfix techniques to hide malicious commands in the Windows Run dialog box from naked eyes.
references:
    - https://expel.com/blog/cache-smuggling-when-a-picture-isnt-a-thousand-words/
    - https://github.com/JohnHammond/recaptcha-phish
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-11-04
tags:
    - attack.execution
    - attack.stealth
    - attack.t1204.004
    - attack.t1027.010
logsource:
    category: registry_set
    product: windows
detection:
    selection_key:
        TargetObject|contains: '\Software\Microsoft\Windows\CurrentVersion\Explorer\RunMRU\'
        Details|contains: '#'
    selection_space_variation:
        Details|contains:
            - '            ' # En Quad (U+2000)
            - '            ' # Em Quad (U+2001)
            - '            ' # En Space (U+2002)
            - '            ' # Em Space (U+2003)
            - '            ' # Three-Per-Em Space (U+2004)
            - '            ' # Four-Per-Em Space (U+2005)
            - '            ' # Six-Per-Em Space (U+2006)
            - '            ' # Figure Space (U+2007)
            - '            ' # Punctuation Space (U+2008)
            - '            ' # Thin Space (U+2009)
            - '            ' # Hair Space (U+200A)
            - '            ' # No-Break Space (U+00A0)
            - '            ' # Normal space
    condition: all of selection_*
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_key`

selection_key:
    TargetObject|contains: '\Software\Microsoft\Windows\CurrentVersion\Explorer\RunMRU\'
    Details|contains: '#'

Stage 2: `selection_space_variation`

selection_space_variation:
    Details|contains:
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '
        - '            '

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
`Details`	match	corpus 2 (sigma 2) `#` corpus 3 (sigma 3) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2) corpus 2 (sigma 2)
`TargetObject`	match	`\Software\Microsoft\Windows\CurrentVersion\Explorer\RunMRU\` corpus 2 (sigma 2)

`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)

Suspicious Space Characters in RunMRU Registry Path - ClickFix

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_key`

Stage 2: `selection_space_variation`

Indicators

Keyboard shortcuts

Search operators

Suspicious Space Characters in RunMRU Registry Path - ClickFix

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_key

Stage 2: selection_space_variation

Indicators

Stage 0: `condition`

Stage 1: `selection_key`

Stage 2: `selection_space_variation`