Attachment: Archive contains DLL-loading macro

calendar Sep 11, 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 == "zip"
13            and (
14              any(file.explode(.),
15                  .scan.zip.encrypted == false
16                  // zip contains a dll file
17                  and any(.scan.zip.all_paths, strings.icontains(., "dll"))
18              )
19              and any(file.explode(.),
20                      // macro references a dll file
21                      any(.flavors.yara, strings.like(., "vb_file"))
22                      and any(.scan.strings.strings, strings.icontains(., "dll"))
23              )
24            )
25          )
26          or any(file.explode(.), // fallback for encrypted zips
27                 .scan.zip.encrypted == true
28                 and any(.scan.zip.all_paths, any($file_extensions_macros, strings.icontains(.., .)))
29                 // zip contains a dll file
30                 and any(.scan.zip.all_paths, strings.icontains(., "dll"))
31          )
32          or (
33            .file_extension in~ $file_extensions_common_archives
34            and any(file.explode(.),
35                    any(.flavors.yara, strings.like(., "vb_file"))
36                    and any(.scan.strings.strings, strings.ilike(., "*Lib*.dll*"))
37            )
38            and any(file.explode(.), strings.ilike(.file_extension, "dll"))
39          )
40  )  
41attack_types:
42  - "Malware/Ransomware"
43tactics_and_techniques:
44  - "Exploit"
45  - "LNK"
46  - "Macros"
47  - "Scripting"
48detection_methods:
49  - "Archive analysis"
50  - "File analysis"
51  - "Macro analysis"
52  - "YARA"
53id: "3a193f5f-1596-54d8-8fd7-1e09e63e6ea4"
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