Suspicious Double Extension File Execution

Status: stable
Severity: high
Log source: product windows, category process_creation
Author: Florian Roth (Nextron Systems), @blu3_team (idea), Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects suspicious use of an .exe extension after a non-executable file extension like .pdf.exe, a set of spaces or underlines to cloak the executable file in spear phishing campaigns

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1566.001` Phishing: Spearphishing Attachment

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation
Security-Auditing	Event ID 4688	A new process has been created.

Rule body yaml

title: Suspicious Double Extension File Execution
id: 1cdd9a09-06c9-4769-99ff-626e2b3991b8
related:
    - id: 5e6a80c8-2d45-4633-9ef4-fa2671a39c5c # ParentImage/ParentCommandLine
      type: similar
status: stable
description: Detects suspicious use of an .exe extension after a non-executable file extension like .pdf.exe, a set of spaces or underlines to cloak the executable file in spear phishing campaigns
references:
    - https://blu3-team.blogspot.com/2019/06/misleading-extensions-xlsexe-docexe.html
    - https://twitter.com/blackorbird/status/1140519090961825792
    - https://cloud.google.com/blog/topics/threat-intelligence/cybercriminals-weaponize-fake-ai-websites
author: Florian Roth (Nextron Systems), @blu3_team (idea), Nasreddine Bencherchali (Nextron Systems)
date: 2019-06-26
modified: 2025-05-30
tags:
    - attack.initial-access
    - attack.t1566.001
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '      .exe'
            - '______.exe'
            - '.doc.exe'
            - '.doc.js'
            - '.docx.exe'
            - '.docx.js'
            - '.gif.exe'
            - '.jpeg.exe'
            - '.jpg.exe'
            - '.mkv.exe'
            - '.mov.exe'
            - '.mp3.exe'
            - '.mp4.exe'
            - '.pdf.exe'
            - '.pdf.js'
            - '.png.exe'
            - '.ppt.exe'
            - '.ppt.js'
            - '.pptx.exe'
            - '.pptx.js'
            - '.rtf.exe'
            - '.rtf.js'
            - '.svg.exe'
            - '.txt.exe'
            - '.txt.js'
            - '.xls.exe'
            - '.xls.js'
            - '.xlsx.exe'
            - '.xlsx.js'
            - '⠀⠀⠀⠀⠀⠀.exe' # Unicode Space Character: Braille Pattern Blank (Unicode: U+2800)
        CommandLine|contains:
            - '      .exe'
            - '______.exe'
            - '.doc.exe'
            - '.doc.js'
            - '.docx.exe'
            - '.docx.js'
            - '.gif.exe'
            - '.jpeg.exe'
            - '.jpg.exe'
            - '.mkv.exe'
            - '.mov.exe'
            - '.mp3.exe'
            - '.mp4.exe'
            - '.pdf.exe'
            - '.pdf.js'
            - '.png.exe'
            - '.ppt.exe'
            - '.ppt.js'
            - '.pptx.exe'
            - '.pptx.js'
            - '.rtf.exe'
            - '.rtf.js'
            - '.svg.exe'
            - '.txt.exe'
            - '.txt.js'
            - '.xls.exe'
            - '.xls.js'
            - '.xlsx.exe'
            - '.xlsx.js'
            - '⠀⠀⠀⠀⠀⠀.exe' # Unicode Space Character: Braille Pattern Blank (Unicode: U+2800)
    condition: selection
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    Image|endswith:
        - '      .exe'
        - '______.exe'
        - '.doc.exe'
        - '.doc.js'
        - '.docx.exe'
        - '.docx.js'
        - '.gif.exe'
        - '.jpeg.exe'
        - '.jpg.exe'
        - '.mkv.exe'
        - '.mov.exe'
        - '.mp3.exe'
        - '.mp4.exe'
        - '.pdf.exe'
        - '.pdf.js'
        - '.png.exe'
        - '.ppt.exe'
        - '.ppt.js'
        - '.pptx.exe'
        - '.pptx.js'
        - '.rtf.exe'
        - '.rtf.js'
        - '.svg.exe'
        - '.txt.exe'
        - '.txt.js'
        - '.xls.exe'
        - '.xls.js'
        - '.xlsx.exe'
        - '.xlsx.js'
        - '⠀⠀⠀⠀⠀⠀.exe'
    CommandLine|contains:
        - '      .exe'
        - '______.exe'
        - '.doc.exe'
        - '.doc.js'
        - '.docx.exe'
        - '.docx.js'
        - '.gif.exe'
        - '.jpeg.exe'
        - '.jpg.exe'
        - '.mkv.exe'
        - '.mov.exe'
        - '.mp3.exe'
        - '.mp4.exe'
        - '.pdf.exe'
        - '.pdf.js'
        - '.png.exe'
        - '.ppt.exe'
        - '.ppt.js'
        - '.pptx.exe'
        - '.pptx.js'
        - '.rtf.exe'
        - '.rtf.js'
        - '.svg.exe'
        - '.txt.exe'
        - '.txt.js'
        - '.xls.exe'
        - '.xls.js'
        - '.xlsx.exe'
        - '.xlsx.js'
        - '⠀⠀⠀⠀⠀⠀.exe'

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	`.exe` `.doc.exe` `.doc.js` `.docx.exe` `.docx.js` `.gif.exe` `.jpeg.exe` `.jpg.exe` `.mkv.exe` `.mov.exe` `.mp3.exe` `.mp4.exe` `.pdf.exe` `.pdf.js` `.png.exe` `.ppt.exe` `.ppt.js` `.pptx.exe` `.pptx.js` `.rtf.exe` `.rtf.js` `.svg.exe` `.txt.exe` `.txt.js` `.xls.exe` `.xls.js` `.xlsx.exe` `.xlsx.js` `______.exe` `⠀⠀⠀⠀⠀⠀.exe`
`Image`	ends_with	`.exe` `.doc.exe` `.doc.js` `.docx.exe` `.docx.js` `.gif.exe` `.jpeg.exe` `.jpg.exe` `.mkv.exe` `.mov.exe` `.mp3.exe` `.mp4.exe` `.pdf.exe` `.pdf.js` `.png.exe` `.ppt.exe` `.ppt.js` `.pptx.exe` `.pptx.js` `.rtf.exe` `.rtf.js` `.svg.exe` `.txt.exe` `.txt.js` `.xls.exe` `.xls.js` `.xlsx.exe` `.xlsx.js` `______.exe` `⠀⠀⠀⠀⠀⠀.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)

Suspicious Double Extension File Execution

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Indicators

Keyboard shortcuts

Search operators

Suspicious Double Extension File Execution

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Indicators

Stage 0: `condition`

Stage 1: `selection`