Potential File Extension Spoofing Using Right-to-Left Override

Status: test
Severity: high
Log source: product windows, category file_event
Author: Jonathan Peters (Nextron Systems), Florian Roth (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects suspicious filenames that contain a right-to-left override character and a potentially spoofed file extensions.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1036.002` Masquerading: Right-to-Left Override

Event coverage

Provider	Event	Title
Sysmon	Event ID 11	FileCreate

Rule body yaml

title: Potential File Extension Spoofing Using Right-to-Left Override
id: 979baf41-ca44-4540-9d0c-4fcef3b5a3a4
related:
    - id: ad691d92-15f2-4181-9aa4-723c74f9ddc3
      type: derived
status: test
description: |
    Detects suspicious filenames that contain a right-to-left override character and a potentially spoofed file extensions.
references:
    - https://redcanary.com/blog/right-to-left-override/
    - https://www.malwarebytes.com/blog/news/2014/01/the-rtlo-method
    - https://tria.ge/241015-l98snsyeje/behavioral2
    - https://www.unicode.org/versions/Unicode5.2.0/ch02.pdf
author: Jonathan Peters (Nextron Systems), Florian Roth (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2024-11-17
modified: 2026-03-20
tags:
    - attack.execution
    - attack.stealth
    - attack.t1036.002
logsource:
    category: file_event
    product: windows
detection:
    selection_rtlo_unicode:
        TargetFilename|contains:
            - '\u202e'  # Unicode RTLO character
            - '[U+202E]'
            # Real char U+202E copied/pasted below
            - '‮'
    selection_extensions:
        TargetFilename|contains:
            - '3pm.'  # Reversed `.mp3`
            - '4pm.'  # Reversed `.mp4`
            - 'cod.'  # Reversed `.doc`
            - 'fdp.'  # Reversed `.pdf`
            - 'ftr.'  # Reversed `.rtf`
            - 'gepj.'  # Reversed `.jpeg`
            - 'gnp.'  # Reversed `.png`
            - 'gpj.'  # Reversed `.jpg`
            - 'ism.'  # Reversed `.msi`
            - 'lmth.'  # Reversed `.html`
            - 'nls.' # Reversed `.sln`
            - 'piz.'  # Reversed `.zip`
            - 'slx.'  # Reversed `.xls`
            - 'tdo.'  # Reversed `.odt`
            - 'vsc.'  # Reversed `.csv`
            - 'vwm.'  # Reversed `.wmv`
            - 'xcod.'  # Reversed `.docx`
            - 'xslx.'  # Reversed `.xlsx`
            - 'xtpp.'  # Reversed `.pptx`
    condition: all of selection_*
falsepositives:
    - Filenames that contains scriptures such as arabic or hebrew might make use of this character
level: high
regression_tests_path: regression_data/rules/windows/file/file_event/file_event_win_susp_right_to_left_override_extension_spoofing/info.yml

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_rtlo_unicode`

selection_rtlo_unicode:
    TargetFilename|contains:
        - '\u202e'
        - '[U+202E]'
        - '‮'

Stage 2: `selection_extensions`

selection_extensions:
    TargetFilename|contains:
        - '3pm.'
        - '4pm.'
        - 'cod.'
        - 'fdp.'
        - 'ftr.'
        - 'gepj.'
        - 'gnp.'
        - 'gpj.'
        - 'ism.'
        - 'lmth.'
        - 'nls.'
        - 'piz.'
        - 'slx.'
        - 'tdo.'
        - 'vsc.'
        - 'vwm.'
        - 'xcod.'
        - 'xslx.'
        - 'xtpp.'

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`	match	`3pm.` `4pm.` `[U+202E]` `\u202e` `cod.` `fdp.` `ftr.` `gepj.` `gnp.` `gpj.` `ism.` `lmth.` `nls.` `piz.` `slx.` `tdo.` `vsc.` `vwm.` `xcod.` `xslx.` `xtpp.` `‮` corpus 2 (sigma 1, elastic 1)

`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)

Potential File Extension Spoofing Using Right-to-Left Override

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_rtlo_unicode`

Stage 2: `selection_extensions`

Indicators

Keyboard shortcuts

Search operators

Potential File Extension Spoofing Using Right-to-Left Override

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_rtlo_unicode

Stage 2: selection_extensions

Indicators

Stage 0: `condition`

Stage 1: `selection_rtlo_unicode`

Stage 2: `selection_extensions`