Credential phishing: Generic document share template

name: "Credential phishing: Generic document share template"
description: "Detects messages that incorporate recipient-specific information (email domain, local part, or domain elements) alongside document-themed Unicode symbols and keywords. The rule identifies various targeting patterns including greeting-based personalization, attention-grabbing prefixes and multiple recipient elements. It also catches broken template attacks where recipient placeholders remain visible."
type: "rule"
severity: "low"
source: |
  type.inbound
  and (
    // nlu capture for wide scope of greetings to reduce evasion
    any(filter(ml.nlu_classifier(body.current_thread.text).entities,
               .name == "greeting"
        ),
        any([
              recipients.to[0].email.domain.sld,
              recipients.to[0].email.local_part,
              recipients.to[0].email.domain.domain
            ],
            strings.icontains(body.current_thread.text,
                              strings.concat(..text, " ", .)
            )
        )
    )
    or any([
             recipients.to[0].email.domain.sld,
             recipients.to[0].email.local_part,
             recipients.to[0].email.domain.domain
           ],
           // strings logic for non-greeting body starter
           strings.icontains(body.current_thread.text,
                             strings.concat("attn: ", .)
           )
           // strings logic for recipient as starter
           or strings.icontains(body.current_thread.text,
                                strings.concat(., " balance statement")
           )
    )
    // count of all recipient elements is higher 2 or greater
    or length(filter([
                       recipients.to[0].email.domain.sld,
                       recipients.to[0].email.local_part,
                       recipients.to[0].email.domain.domain
                     ],
                     strings.icontains(body.current_thread.text, .)
              )
    ) >= 2
  
    // logic for broken attack
    or any(ml.nlu_classifier(body.current_thread.text).entities,
           .name == "recipient" and regex.icontains(.text, '[{}]')
    )
  )
  
  // unicode + keyword generic template
  and (
    regex.icontains(body.current_thread.text,
                    '(?:\x{270e}|\x{270f}|\x{2710}|\x{270d}|\x{1f589}|\x{1F4C4}|\x{1F4D1}|\x{1F4C1}|\x{1F4EC}).{0,15}(?:document|completion|remit|review|statement|agree|shar(?:ed|ing)|receiv|\bmail\b)',
                    '(?:document|completion|remit|review|statement|agree|shar(?:ed|ing)|receiv|\bmail\b).{0,15}(?:\x{270e}|\x{270f}|\x{2710}|\x{270d}|\x{1f589}|\x{1F4C4}|\x{1F4D1}|\x{1F4C1}|\x{1F4EC})'
    )
    // negate sharepoint paths with unicode
    and not any(body.links,
                regex.icontains(.display_url.path,
                                '(?:\x{270e}|\x{270f}|\x{2710}|\x{270d}|\x{1f589}|\x{1F4C4}|\x{1F4D1}|\x{1F4C1}|\x{1F4EC})'
                )
    )
  )
  
  // nlu negation for FP's
  and any(ml.nlu_classifier(body.current_thread.text).intents, .name != "benign")
  
  // negate highly trusted sender domains unless they fail DMARC authentication
  and (
    (
      sender.email.domain.root_domain in $high_trust_sender_root_domains
      and not headers.auth_summary.dmarc.pass
    )
    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
  )

tags:
  - "Attack surface reduction"
attack_types:
  - "BEC/Fraud"
  - "Credential Phishing"
tactics_and_techniques:
  - "Social engineering"
  - "Evasion"
detection_methods:
  - "Content analysis"
  - "Natural Language Understanding"
id: "f5bee657-53bc-501f-9b7a-ea51da73a716"