sublimehighRule

Google share notification with suspicious comments

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.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1534

initial-access

Detection Query

type.inbound
and 
// message is from google actual
sender.email.domain.domain == 'google.com'
and (
  sender.email.local_part == "drive-shares-noreply"
  or sender.email.local_part == "drive-shares-dm-noreply"
)
// contains a comment
and strings.icontains(body.html.raw,
                      '<div style="margin-top:24px; color:#5F6368">'
)
// those comments contain what appears to be an email
and (
  regex.icontains(body.html.raw,
                  '</div>\s*<div style="margin-top:24px; color:#5F6368">\s*(?:RE|FWD?)\s*:'
  )
  // the comment contains wording that relates to sharing a file
  // the list before being sent through regexp-assemble
  //   "request to view", "shared a file",   "sent you a file",
  //   "file access request", "view shared document",
  //   "pending file request", "document shared", "view a file",
  //   "file sent to you", "invited to view", "file access invite",
  //   "click to view", "open shared file", "drive file request"
  or regex.icontains(body.html.raw,
                     '</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>'
  )
)
// not where the sender display name of the message is within org_display_names
and not (
  // the message is from google actual
  sender.email.email in (
    'comments-noreply@docs.google.com',
    'drive-shares-dm-noreply@google.com',
    'drive-shares-noreply@google.com',
    'calendar-notification@google.com'
  )
  and headers.auth_summary.dmarc.pass
  // but the sender display name is within org_display_names
  and (
    any(regex.iextract(sender.display_name,
                       '^(?P<sender_display_name>.*)\((?:via )?Google'
        ),
        .named_groups["sender_display_name"] in~ $org_display_names
    )
    or (
      length(headers.reply_to) == 1
      and all(headers.reply_to, .email.domain.domain in $org_domains)
    )
  )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Google share notification with suspicious comments"
description: "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."
type: "rule"
severity: "high"
source: |
  type.inbound
  and 
  // message is from google actual
  sender.email.domain.domain == 'google.com'
  and (
    sender.email.local_part == "drive-shares-noreply"
    or sender.email.local_part == "drive-shares-dm-noreply"
  )
  // contains a comment
  and strings.icontains(body.html.raw,
                        '<div style="margin-top:24px; color:#5F6368">'
  )
  // those comments contain what appears to be an email
  and (
    regex.icontains(body.html.raw,
                    '</div>\s*<div style="margin-top:24px; color:#5F6368">\s*(?:RE|FWD?)\s*:'
    )
    // the comment contains wording that relates to sharing a file
    // the list before being sent through regexp-assemble
    //   "request to view", "shared a file",   "sent you a file",
    //   "file access request", "view shared document",
    //   "pending file request", "document shared", "view a file",
    //   "file sent to you", "invited to view", "file access invite",
    //   "click to view", "open shared file", "drive file request"
    or regex.icontains(body.html.raw,
                       '</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>'
    )
  )
  // not where the sender display name of the message is within org_display_names
  and not (
    // the message is from google actual
    sender.email.email in (
      'comments-noreply@docs.google.com',
      'drive-shares-dm-noreply@google.com',
      'drive-shares-noreply@google.com',
      'calendar-notification@google.com'
    )
    and headers.auth_summary.dmarc.pass
    // but the sender display name is within org_display_names
    and (
      any(regex.iextract(sender.display_name,
                         '^(?P<sender_display_name>.*)\((?:via )?Google'
          ),
          .named_groups["sender_display_name"] in~ $org_display_names
      )
      or (
        length(headers.reply_to) == 1
        and all(headers.reply_to, .email.domain.domain in $org_domains)
      )
    )
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Impersonation: VIP"
  - "Free file host"
detection_methods:
  - "HTML analysis"
  - "Header analysis"
  - "Sender analysis"
  - "Content analysis"
id: "c69c9924-33ed-564d-9ec3-5b3c5e1321c5"