Attachment: Any HTML file within archive (unsolicited)

 1name: "Attachment: Any HTML file within archive (unsolicited)"
 2description: |
 3  Recursively scans archives to detect HTML files from unsolicited senders. 
 4
 5  HTML files can be used for HTML smuggling and embedded in archives to evade detection.  
 6references:
 7  - "https://twitter.com/executemalware/status/1537569201577156611"
 8type: "rule"
 9severity: "medium"
10source: |
11  type.inbound
12  and any(attachments,
13          .file_extension in~ $file_extensions_common_archives
14          and any(file.explode(.), .depth > 0 and .file_extension in~ ("html", "htm"))
15  )
16  and (
17    not profile.by_sender().solicited
18    or (
19      profile.by_sender().any_messages_malicious_or_spam
20    )
21  )
22
23  and not profile.by_sender().any_false_positives  
24tags:
25  - "Attack surface reduction"
26attack_types:
27  - "Credential Phishing"
28  - "Malware/Ransomware"
29tactics_and_techniques:
30  - "Evasion"
31  - "HTML smuggling"
32detection_methods:
33  - "Archive analysis"
34  - "File analysis"
35id: "6a67c02c-d405-531e-850a-1722849c5fe4"