Download by Process with Double File Extension

calendar Jan 30, 2023 · attack.defense_evasion attack.command_and_control attack.t1218 attack.t1218.009 attack.t1071 attack.t1071.004  ·
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Detects downloads by processes with double file extensions, a common method of masquerading or obfuscating a file type in malware delivery. Observed in early 2023 AsyncRAT/Quasar malware delivery using malicious OneNote files.

Sigma rule (View on GitHub)

 1title: Download by Process with Double File Extension
 2id: 60dbde0d-57dc-40e4-a95c-3488f319f216
 3status: experimental
 4description: Detects downloads by processes with double file extensions, a common method of masquerading or obfuscating a file type in malware delivery. Observed in early 2023 AsyncRAT/Quasar malware delivery using malicious OneNote files.
 5references:
 6    - https://isc.sans.edu/diary/rss/29470
 7    - Home lab research by Micah Babinski
 8author: Micah Babinski, @micahbabinski
 9date: 2023/01/30
10tags:
11    - attack.defense_evasion
12    - attack.command_and_control
13    - attack.t1218
14    - attack.t1218.009
15    - attack.t1071
16    - attack.t1071.004
17logsource:
18    category: create_stream_hash
19    product: windows
20detection:
21    selection:
22        Image|re: ^.*\\[a-zA-Z0-9]*\.[a-zA-Z0-9]*\.[a-zA-Z0-9]*$
23    condition: selection
24falsepositives:
25    - Unknown
26level: high```

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