Service abuse: DocuSign share from an unsolicited reply-to address

 1name: "Service abuse: DocuSign share from an unsolicited reply-to address"
 2description: "DocuSign shares which contain a reply-to address or domain that has not been previously observed by the recipient organization."
 3type: "rule"
 4severity: "medium"
 5source: |
 6  type.inbound
 7  
 8  // message is from docusign actual
 9  and sender.email.domain.root_domain == 'docusign.net'
10  and not any(headers.reply_to, .email.domain.domain == 'docusign.com')
11  and (headers.auth_summary.spf.pass or headers.auth_summary.dmarc.pass)
12  
13  // not a completed DocuSign
14  // reminders are sent automatically and can be just as malicious as the initial
15  // users often decline malicious ones
16  and not strings.istarts_with(subject.subject, "Completed: ")
17  and not strings.istarts_with(subject.subject, "Here is your signed document: ")
18  and not strings.istarts_with(subject.subject, "Voided: ")
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 address rarely seen in org
26  and beta.profile.by_reply_to().prevalence in~ ("new", "rare")
27  
28  // reply-to email address has never been sent an email by the org
29  and not beta.profile.by_reply_to().solicited
30  
31  // do not match if the reply_to address has been observed as a reply_to address
32  // of a message that has been classified as benign
33  and not beta.profile.by_reply_to().any_messages_benign  
34tags:
35 - "Attack surface reduction"
36attack_types:
37  - "Credential Phishing"
38tactics_and_techniques:
39  - "Evasion"
40  - "Free file host"
41  - "Social engineering"
42detection_methods:
43  - "Content analysis"
44  - "Header analysis"
45  - "Sender analysis"
46id: "2f12d616-f47a-5259-8946-ac2e01940f6f"