Csc.EXE Execution Form Potentially Suspicious Parent

calendar Nov 6, 2023 · attack.execution attack.t1059.005 attack.t1059.007 attack.defense_evasion attack.t1218.005 attack.t1027.004  ·
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Detects a potentially suspicious parent of "csc.exe", which could be a sign of payload delivery.

Sigma rule (View on GitHub)

 1title: Csc.EXE Execution Form Potentially Suspicious Parent
 2id: b730a276-6b63-41b8-bcf8-55930c8fc6ee
 3status: test
 4description: Detects a potentially suspicious parent of "csc.exe", which could be a sign of payload delivery.
 5references:
 6    - https://www.uptycs.com/blog/warzonerat-can-now-evade-with-process-hollowing
 7    - https://reaqta.com/2017/11/short-journey-darkvnc/
 8    - https://www.pwc.com/gx/en/issues/cybersecurity/cyber-threat-intelligence/yellow-liderc-ships-its-scripts-delivers-imaploader-malware.html
 9author: Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems), X__Junior (Nextron Systems)
10date: 2019/02/11
11modified: 2023/10/27
12tags:
13    - attack.execution
14    - attack.t1059.005
15    - attack.t1059.007
16    - attack.defense_evasion
17    - attack.t1218.005
18    - attack.t1027.004
19logsource:
20    category: process_creation
21    product: windows
22detection:
23    selection_img:
24        - Image|endswith: '\csc.exe'
25        - OriginalFileName: 'csc.exe'
26    selection_parent_generic:
27        ParentImage|endswith:
28            - '\cscript.exe'
29            - '\excel.exe'
30            - '\mshta.exe'
31            - '\onenote.exe'
32            - '\outlook.exe'
33            - '\powerpnt.exe'
34            - '\winword.exe'
35            - '\wscript.exe'
36    selection_parent_powershell:
37        ParentImage|endswith:
38            - '\powershell.exe'
39            - '\pwsh.exe'
40        ParentCommandLine|contains:
41            - '-Encoded '
42            - 'FromBase64String'
43    selection_parent_susp_location:
44        - ParentCommandLine|re: '([Pp]rogram[Dd]ata|%([Ll]ocal)?[Aa]pp[Dd]ata%|\\[Aa]pp[Dd]ata\\([Ll]ocal(Ll]ow)?|[Rr]oaming))\\[^\\]{1,256}$'
45        - ParentCommandLine|contains:
46              - ':\PerfLogs\'
47              - ':\Users\Public\'
48              - ':\Windows\Temp\'
49              - '\Temporary Internet'
50        - ParentCommandLine|contains|all:
51              - ':\Users\'
52              - '\Favorites\'
53        - ParentCommandLine|contains|all:
54              - ':\Users\'
55              - '\Favourites\'
56        - ParentCommandLine|contains|all:
57              - ':\Users\'
58              - '\Contacts\'
59        - ParentCommandLine|contains|all:
60              - ':\Users\'
61              - '\Pictures\'
62    filter_main_programfiles:
63        # Note: this is a generic filter. You could baseline execution in your env for a more robust rule
64        ParentImage|startswith:
65            - 'C:\Program Files (x86)\' # https://twitter.com/gN3mes1s/status/1206874118282448897
66            - 'C:\Program Files\' # https://twitter.com/gN3mes1s/status/1206874118282448897
67    filter_main_sdiagnhost:
68        ParentImage: 'C:\Windows\System32\sdiagnhost.exe' # https://twitter.com/gN3mes1s/status/1206874118282448897
69    filter_main_w3p:
70        ParentImage: 'C:\Windows\System32\inetsrv\w3wp.exe' # https://twitter.com/gabriele_pippi/status/1206907900268072962
71    filter_optional_chocolatey:
72        ParentImage: 'C:\ProgramData\chocolatey\choco.exe' # Chocolatey https://chocolatey.org/
73    filter_optional_defender:
74        ParentCommandLine|contains: '\ProgramData\Microsoft\Windows Defender Advanced Threat Protection'
75    filter_optional_ansible:
76        # Note: As ansible is widely used we exclude it with this generic filter.
77        # A better option would be to filter based on script content basis or other marker while hunting
78        ParentCommandLine|contains:
79            # '{"failed":true,"msg":"Ansible requires PowerShell v3.0 or newer"}'
80            - 'JwB7ACIAZgBhAGkAbABlAGQAIgA6AHQAcgB1AGUALAAiAG0AcwBnACIAOgAiAEEAbgBzAGkAYgBsAGUAIAByAGUAcQB1AGkAcgBlAHMAIABQAG8AdwBlAHIAUwBoAGUAbABsACAAdgAzAC4AMAAgAG8AcgAgAG4AZQB3AGUAcgAiAH0AJw'
81            - 'cAewAiAGYAYQBpAGwAZQBkACIAOgB0AHIAdQBlACwAIgBtAHMAZwAiADoAIgBBAG4AcwBpAGIAbABlACAAcgBlAHEAdQBpAHIAZQBzACAAUABvAHcAZQByAFMAaABlAGwAbAAgAHYAMwAuADAAIABvAHIAIABuAGUAdwBlAHIAIgB9ACcA'
82            - 'nAHsAIgBmAGEAaQBsAGUAZAAiADoAdAByAHUAZQAsACIAbQBzAGcAIgA6ACIAQQBuAHMAaQBiAGwAZQAgAHIAZQBxAHUAaQByAGUAcwAgAFAAbwB3AGUAcgBTAGgAZQBsAGwAIAB2ADMALgAwACAAbwByACAAbgBlAHcAZQByACIAfQAnA'
83    condition: selection_img and 1 of selection_parent_* and not 1 of filter_main_* and not 1 of filter_optional_*
84falsepositives:
85    - Unknown
86level: high

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