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(.),
15                  .depth > 0 and .file_extension in~ ("html", "htm")
16          )
17  )
18  and (
19    not profile.by_sender().solicited
20    or (profile.by_sender().any_messages_malicious_or_spam)
21  )
22  and not profile.by_sender().any_messages_benign  
23tags:
24  - "Attack surface reduction"
25attack_types:
26  - "Credential Phishing"
27  - "Malware/Ransomware"
28tactics_and_techniques:
29  - "Evasion"
30  - "HTML smuggling"
31detection_methods:
32  - "Archive analysis"
33  - "File analysis"
34id: "6a67c02c-d405-531e-850a-1722849c5fe4"