Attachment: OLE external relationship containing file scheme link to executable filetype

 1name: "Attachment: OLE external relationship containing file scheme link to executable filetype"
 2description: "This rule identifies attachments containing file scheme links pointing to executable file types, a common indicator of malware distribution. It applies to various suspicious file extensions and archive formats, aiming to prevent the initiation and execution of malicious software."
 3type: "rule"
 4severity: "high"
 5source: |
 6  type.inbound
 7  and any(attachments,
 8          (
 9            .file_extension in~ $file_extensions_macros
10            or .file_extension in~ $file_extensions_common_archives
11            or (
12              .file_extension is null
13              and .file_type == "unknown"
14              and .content_type == "application/octet-stream"
15              and .size < 100000000
16            )
17          )
18          and length(file.oletools(.).relationships) < 500
19          and any(file.oletools(.).relationships,
20                  .target_url.scheme == "file"
21                  and regex.icontains(.target_url.path,
22                                      '\.(action|ahk|apk|app|appimage|applescript|bat|bin|cab|cmd|command|cpl|dll|dmg|exe|gadget|hta|inf|ins|ipa|isu|jar|job|js|jse|lnk|msi|msp|paf|pif|ps1|rgs|run|scr|sct|sh|shb|vb|vbe|vbs)($|[^\w])'
23                  )
24          )
25  )
26  and (
27    not profile.by_sender().any_false_positives
28    or profile.by_sender().any_messages_malicious_or_spam
29  )
30    
31tags:
32  - "Attack surface reduction"
33  - "PikaBot"
34  - "DarkGate"
35attack_types:
36  - "Malware/Ransomware"
37tactics_and_techniques:
38  - "Evasion"
39detection_methods:
40  - "Archive analysis"
41  - "Content analysis"
42  - "OLE analysis"
43  - "Sender analysis"
44
45id: "33bf6fd4-b170-5da2-808a-ffe74af6e21b"