File sharing link from suspicious sender domain

A file sharing link in the body sent from a suspicious sender domain.

Sublime rule (View on GitHub)

 1name: "File sharing link from suspicious sender domain"
 2description: |
 3    A file sharing link in the body sent from a suspicious sender domain.
 4type: "rule"
 5severity: "medium"
 6source: |
 7  type.inbound
 8  and any(body.links,
 9          (
10            .href_url.domain.domain in $free_file_hosts
11            or .href_url.domain.root_domain in $free_file_hosts
12          )
13          // remove free_file_hosts used to host images as links
14          and not any($file_types_images,
15                      strings.iends_with(..href_url.url, strings.concat('.', .))
16          )
17  )
18  and sender.email.domain.tld in $suspicious_tlds
19  and (
20    not profile.by_sender().solicited
21    or (
22      profile.by_sender().any_messages_malicious_or_spam
23      and not profile.by_sender().any_false_positives
24    )
25  )  
26
27tags:
28  - "Attack surface reduction"
29attack_types:
30  - "Credential Phishing"
31  - "Malware/Ransomware"
32tactics_and_techniques:
33  - "Free file host"
34detection_methods:
35  - "Sender analysis"
36  - "URL analysis"
37id: "95f20354-3091-537e-9fe0-80ea8b64913b"

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