MMC Executing Files with Reversed Extensions Using RTLO Abuse

experimentalhigh

log source: windows · process_creationauthor Swachchhanda Shrawan Poudel (Nextron Systems)date 2025-02-05

description

What this is, in brief.

Detects malicious behavior where the MMC utility (`mmc.exe`) executes files with reversed extensions caused by Right-to-Left Override (RLO) abuse, disguising them as document formats.

rule source (YAML)

title: MMC Executing Files with Reversed Extensions Using RTLO Abuse
id: 9cfe4b27-1e56-48b4-b7a8-d46851c91a44
status: experimental
description: Detects malicious behavior where the MMC utility (`mmc.exe`) executes files with reversed extensions caused by Right-to-Left Override (RLO) abuse, disguising them as document formats.
references:
    - https://www.unicode.org/versions/Unicode5.2.0/ch02.pdf
    - https://en.wikipedia.org/wiki/Right-to-left_override
    - https://tria.ge/241015-l98snsyeje/behavioral2
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-02-05
tags:
    - attack.execution
    - attack.stealth
    - attack.t1204.002
    - attack.t1218.014
    - attack.t1036.002
logsource:
    category: process_creation
    product: windows
detection:
    selection_image:
        - Image|endswith: '\mmc.exe'
        - OriginalFileName: 'MMC.exe'
    selection_commandline:
        CommandLine|contains: # While looking at these files the prefix of their name will look something like csm.pdf, but in reality it is msc file
            - 'cod.msc'  # Reversed `.doc`
            - 'fdp.msc'  # Reversed `.pdf`
            - 'ftr.msc'  # Reversed `.rtf`
            - 'lmth.msc'  # Reversed `.html`
            - 'slx.msc'  # Reversed `.xls`
            - 'tdo.msc'  # Reversed `.odt`
            - 'xcod.msc'  # Reversed `.docx`
            - 'xslx.msc'  # Reversed `.xlsx`
            - 'xtpp.msc'  # Reversed `.pptx`
    condition: all of selection_*
falsepositives:
    - Legitimate administrative actions using MMC to execute misnamed `.msc` files.
    - Unconventional but non-malicious usage of RLO or reversed extensions.
level: high

detects techniques (3)

ATT&CK techniques this enables or maps to.

references

External citations — patches, advisories, analysis.