Google Share Notification with Suspicious Comments

 1name: "Google Share Notification with Suspicious Comments"
 2description: "This detection rule matches on messages which contain suspicious language within the comments of a Google share notification.  Suspicious content within the comments section of the notification is deemed as email abbreviations such as FW:, FWD:, and RE: or by containing words that reference a file share."
 3type: "rule"
 4severity: "high"
 5source: |
 6  type.inbound and
 7  // message is from google actual
 8  sender.email.domain.domain == 'google.com'
 9  and (
10    sender.email.local_part == "drive-shares-noreply"
11    or sender.email.local_part == "drive-shares-dm-noreply"
12  )
13  // contains a comment
14  and strings.icontains(body.html.raw,
15                        '<div style="margin-top:24px; color:#5F6368">'
16  )
17  // those comments contain what appears to be an email
18  and (
19    regex.icontains(body.html.raw,
20                    '</div>\s*<div style="margin-top:24px; color:#5F6368">\s*(?:RE|FWD?)\s*:'
21    )
22    // the comment contains wording that relates to sharing a file
23    // the list before being sent through regexp-assemble
24    //   "request to view", "shared a file",   "sent you a file",
25    //   "file access request", "view shared document",
26    //   "pending file request", "document shared", "view a file",
27    //   "file sent to you", "invited to view", "file access invite",
28    //   "click to view", "open shared file", "drive file request"
29    or regex.icontains(body.html.raw,
30                       '</div>\s*<div style="margin-top:24px; color:#5F6368">[^<]*(?:<[^\/][^<]*)*(?:file (?:access (?:request|invite)|sent to you)|(?:s(?:ent you|hared) a|open shared) file|d(?:rive file request|ocument shared)|(?:invited|request|click) to view|view (?:shared document|a file)|pending file request)[^<]*(?:<[^\/][^<]*)*</div>\s*</td>'
31    )
32  )
33  // not where the sender display name of the message is within org_display_names
34  and not (
35    // the message is from google actual
36    sender.email.email in (
37      'comments-noreply@docs.google.com',
38      'drive-shares-dm-noreply@google.com',
39      'drive-shares-noreply@google.com',
40      'calendar-notification@google.com'
41    )
42    and headers.auth_summary.dmarc.pass
43    // but the sender display name is within org_display_names
44    and any($org_display_names,
45            strings.istarts_with(sender.display_name,
46                                 strings.concat(., " (via Google ")
47            )
48            or strings.istarts_with(sender.display_name,
49                                    strings.concat(., " (Google ")
50            )
51    )
52  )  
53attack_types:
54  - "Credential Phishing"
55tactics_and_techniques:
56  - "Impersonation: VIP"
57  - "Free file host"
58detection_methods:
59  - "HTML analysis"
60  - "Header analysis"
61  - "Sender analysis"
62  - "Content analysis"
63id: "c69c9924-33ed-564d-9ec3-5b3c5e1321c5"