Attachment: Archive contains DLL-loading macro

calendar Dec 28, 2023  ยท
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An attacker could send a trusted and signed document that references an untrusted DLL file, which will be loaded by the signed document.

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 1name: "Attachment: Archive contains DLL-loading macro"
 2description: |
 3    An attacker could send a trusted and signed document that references an untrusted DLL file, which will be loaded by the signed document.
 4references:
 5  - "https://outflank.nl/blog/2023/04/25/so-you-think-you-can-block-macros"
 6type: "rule"
 7severity: "high"
 8source: |
 9  type.inbound
10  and any(attachments,
11          (
12            .file_extension in~ $file_extensions_common_archives
13            or .file_type == "rar"
14          )
15          and (
16            (
17              any(file.explode(.),
18                  .scan.zip.encrypted == false
19                  // zip contains a dll file
20                  and any(.scan.zip.all_paths, strings.icontains(., "dll"))
21              )
22              and any(file.explode(.),
23                      // macro references a dll file
24                      any(.flavors.yara, strings.like(., "vb_file"))
25                      and any(.scan.strings.strings, strings.icontains(., "dll"))
26              )
27            )
28            or any(file.explode(.), // fallback for encrypted zips
29                   .scan.zip.encrypted == true
30                   and any(.scan.zip.all_paths,
31                           any($file_extensions_macros, strings.icontains(.., .))
32                   )
33                   // zip contains a dll file
34                   and any(.scan.zip.all_paths, strings.icontains(., "dll"))
35            )
36            or (
37              any(file.explode(.),
38                  any(.flavors.yara, strings.like(., "vb_file"))
39                  and any(.scan.strings.strings, strings.ilike(., "*Lib*.dll*"))
40              )
41              and any(file.explode(.), strings.ilike(.file_extension, "dll"))
42            )
43          )
44  )  
45attack_types:
46  - "Malware/Ransomware"
47tactics_and_techniques:
48  - "Exploit"
49  - "LNK"
50  - "Macros"
51  - "Scripting"
52detection_methods:
53  - "Archive analysis"
54  - "File analysis"
55  - "Macro analysis"
56  - "YARA"
57id: "3a193f5f-1596-54d8-8fd7-1e09e63e6ea4"
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