Explorer Process Tree Break

calendar Oct 18, 2023 · attack.defense_evasion attack.t1036  ·
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Detects a command line process that uses explorer.exe to launch arbitrary commands or binaries, which is similar to cmd.exe /c, only it breaks the process tree and makes its parent a new instance of explorer spawning from "svchost"

Sigma rule (View on GitHub)

 1title: Explorer Process Tree Break
 2id: 949f1ffb-6e85-4f00-ae1e-c3c5b190d605
 3status: test
 4description: |
 5  Detects a command line process that uses explorer.exe to launch arbitrary commands or binaries,
 6  which is similar to cmd.exe /c, only it breaks the process tree and makes its parent a new instance of explorer spawning from "svchost"  
 7references:
 8    - https://twitter.com/CyberRaiju/status/1273597319322058752
 9    - https://twitter.com/bohops/status/1276357235954909188?s=12
10    - https://twitter.com/nas_bench/status/1535322450858233858
11    - https://securityboulevard.com/2019/09/deobfuscating-ostap-trickbots-34000-line-javascript-downloader/
12author: Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems), @gott_cyber
13date: 2019/06/29
14modified: 2022/09/20
15tags:
16    - attack.defense_evasion
17    - attack.t1036
18logsource:
19    category: process_creation
20    product: windows
21detection:
22    selection:
23        # See CLSID_SeparateMultipleProcessExplorerHost in the registry for reference
24        - CommandLine|contains: '/factory,{75dff2b7-6936-4c06-a8bb-676a7b00b24b}' # This will catch, the new explorer spawning which indicates a process/tree break. But you won't be able to catch the executing process. For that you need historical data
25        # There exists almost infinite possibilities to spawn from explorer. The "/root" flag is just an example
26        # It's better to have the ability to look at the process tree and look for explorer processes with "weird" flags to be able to catch this technique.
27        - CommandLine|contains|all:
28              - 'explorer.exe'
29              - ' /root,'
30    condition: selection
31falsepositives:
32    - Unknown
33level: medium

References

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  • Deobfuscating Ostap: TrickBot’s 34,000 Line JavaScript Downloader

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