Sigma rule: Potential File Extension Spoofing Using Right-to-Left Override

Rule

Title

Potential File Extension Spoofing Using Right-to-Left Override

Status

test

Level

high

Author

Jonathan Peters (Nextron Systems), Florian Roth (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)

Date

2024-11-17

Modified

2026-03-20

File

rules/windows/file/file_event/file_event_win_susp_right_to_left_override_extension_spoofing.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

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

Log source

product

windows

category

file_event

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_*

False positives (as the rule lists them)

• Filenames that contains scriptures such as arabic or hebrew might make use of this character

Tags

• attack.execution
• attack.stealth
• attack.t1036.002

MITRE ATT&CK ids this rule names

• T1036.002

Related rules

• ad691d92-15f2-4181-9aa4-723c74f9ddc3 (derived)

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

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/file/file_event/file_event_win_susp_right_to_left_override_extension_spoofing.yml