Service Abuse: Dropbox Share From New Domain

 1name: "Service Abuse: Dropbox Share From New Domain"
 2description: "This Attack Surface Reduction (ASR) rule matches on Dropbox notifications with recently registered reply-to domains."
 3type: "rule"
 4severity: "medium"
 5source: |
 6  type.inbound
 7  
 8  //  Dropbox actual sending infrastructure
 9  and sender.email.email == "no-reply@dropbox.com"
10  and headers.auth_summary.spf.pass
11  and headers.auth_summary.dmarc.pass
12  and strings.ends_with(headers.auth_summary.spf.details.designator,
13                      '.dropbox.com'
14  )
15  
16  
17  // the message needs to have a reply-to address
18  and length(headers.reply_to) > 0
19
20  // 
21  // This rule makes use of a beta feature and is subject to change without notice
22  // using the beta feature in custom rules is not suggested until it has been formally released
23  // 
24  
25  // reply-to email address has never been sent an email by the org
26  and not beta.profile.by_reply_to().solicited
27  
28  // do not match if the reply_to address has been observed as a reply_to address
29  // of a message that has been classified as benign
30  and not beta.profile.by_reply_to().any_messages_benign
31  
32  // new reply-to domain
33  and any(headers.reply_to,
34          network.whois(.email.domain).days_old < 30
35  )  
36tags:
37 - "Attack surface reduction"
38attack_types:
39  - "Callback Phishing"
40  - "Credential Phishing"
41  - "BEC/Fraud"
42tactics_and_techniques:
43  - "Evasion"
44  - "Social engineering"
45detection_methods:
46  - "Content analysis"
47  - "Sender analysis"
48  - "Header analysis"
49id: "0e664bd9-c3dd-53ca-a912-bb1a627e22ae"