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Description

Detects extortion and sextortion attempts by analyzing the email body text from an untrusted sender.

Sublime Security
Created Aug 17th, 2023 • Last updated Dec 19th, 2025
Source
type.inbound
and length(filter(body.links, .display_text is not null)) < 10
and not (
  ml.nlu_classifier(body.current_thread.text).language == "english"
  and any(ml.nlu_classifier(body.html.display_text).topics,
          .name in (
            "News and Current Events",
            "Newsletters and Digests",
            "Advertising and Promotions"
          )
          and .confidence in ("high", "medium")
  )
)
and (
  (
    any(ml.nlu_classifier(strings.replace_confusables(body.current_thread.text)).intents,
        (.name == "extortion" and .confidence == "high")
    )
    and (
      any(ml.nlu_classifier(strings.replace_confusables(body.current_thread.text
                            )
          ).entities,
          .name == "financial"
          or (
            .name is not null
            and regex.icontains(.text,
                                "cybḛ[rŗřṙȑȓɍʀɼɽг]c[rŗřṙȑȓɍʀɼɽг]imina[lĺļľḷḹḽłƖʟḻ]s"
            )
          )
      )
      or any(ml.nlu_classifier(strings.replace_confusables(body.current_thread.text
                               )
             ).topics,
             .name == "Financial Communications" and .confidence != "low"
      )
    )
  )
  // manual indicators failsafe
  or 3 of (
    // malware terms
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    "(?:(?:spy|[mṁ][aȁ]l)[wŵ][aȁ][rŗ]e|[tŢ][rŗȓ][oố]j[aǻ][nņ]|[rȓ]emote (?:entry|cont[rř]o[lĺ])|infiltrat(?:ed|ion)|backdoor|vi[rṙ]us|intruder|(?:your|the).{0,15}(?:device|system|computer|phone).{0,10}(?:became|was|got|is).{0,5}comprom[ḯiïíįī]sed|prov[ḯiïíįī]d[ḯiïíįī]ng.{0,20}full [aảǡą]ccess)"
    ),
    // actions recorded
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    "(?:p[oộ][rŗ]n|a[dȡ]ult (?:web)?site|webcam|mastu[rŗ]bating|je[rŗ]king off|pleasu[rŗȑ]i[nŋ]g you[rŗṛ]self|getting off|expli[cƈ]it|cl[ḯiïíįī]ps.{0,20}screenshots)"
    ),
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    "(?:pe[rŗ]ve[rŗ]t|pe[rŗ]ve[rŗ]sion|mastu[rŗ]bat)"
    ),
    // a timeframe to pay
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    '[ilo0-9]{2} (?:hou[rŗṝ][sṣ]|uu[rŗ])',
                    '(?:one|tw[oờ]|2|th[rŗ]ee|\d) [dḍ][aảǡą]y[sṣ]?',
                    'set a timer'
    ),
    // a promise from the actor
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    '(?:pe[rŗ]manently|will|I''ll) delete|([rŗ]emove|destroy) (?:[\p{L}\p{M}\p{N}]+\s*){0,4} (?:data|ev[ḯiïįīí]dence|v[ḯiïíįī]deos?)'
    ),
    // a threat from the actor
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    '(?:\bsen[dt]|forward|expose)\s*(?:[\p{L}\p{N}]+\s*){0,5}\s*to\s*(?:[\p{L}\p{N}]+\s*){0,5}(?:contacts|media|family|f[rŗ]iends|coworkers|associates)'
    ),
    // bitcoin language (excluding newsletters)
    (
      regex.icontains(strings.replace_confusables(body.current_thread.text),
                      '[bḆḂ]it[cĉƈ][oöة]i[nņɲ]|\bbtc\b|blockchain'
      )
      // negate cryptocurrency newsletters
      and not (
        any(body.links,
            strings.icontains(.display_text, "unsubscribe")
            and (
              strings.icontains(.href_url.path, "unsubscribe")
              // handle mimecast URL rewrites
              or (
                .href_url.domain.root_domain == 'mimecastprotect.com'
                and strings.icontains(.href_url.query_params,
                                      sender.email.domain.root_domain
                )
              )
            )
        )
      )
    ),
    (
      regex.icontains(strings.replace_confusables(body.current_thread.text),
                      '(?:contact the police|(?:bitcoin|\bbtc\b).{0,20}wallet)'
      )
      and regex.icontains(strings.replace_confusables(body.current_thread.text),
                          '(?:\b[13][a-km-zA-HJ-NP-Z0-9]{24,34}\b)|\bX[1-9A-HJ-NP-Za-km-z]{33}\b|\b(?:0x[a-fA-F0-9]{40})\b|\b[LM3][a-km-zA-HJ-NP-Z1-9]{26,33}\b|\b[48][0-9AB][1-9A-HJ-NP-Za-km-z]{93}\b'
      )
    ),
    regex.icontains(strings.replace_confusables(body.current_thread.text),
                    'bc1q.{0,50}\b'
    )
  )
)
and (
  not profile.by_sender().solicited
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
  or any(headers.hops, any(.fields, .name == "X-Google-Group-Id"))

  // many extortion emails spoof sender domains and fail sender authentication
  or (
    not headers.auth_summary.dmarc.pass
    or headers.auth_summary.dmarc.pass is null
    or not headers.auth_summary.spf.pass
  )
)
// negate legit bounce backs
and not any(ml.nlu_classifier(body.current_thread.text).topics,
            .name in ("Bounce Back and Delivery Failure Notifications")
)
// negate legit forwards and replies
and not (
  (subject.is_reply or subject.is_forward)
  and length(body.previous_threads) > 0
  and (length(headers.references) > 0 or headers.in_reply_to is not null)
)
// negate benign newsletters that mention cyber extortion
and not (
  any(body.links,
      strings.icontains(.display_text, "unsubscribe")
      and strings.icontains(.href_url.path, "unsubscribe")
  )
  // newsletters are typically longer than the average extortion script
  and length(body.current_thread.text) > 2000
)
and length(body.current_thread.text) < 8000
// negate TOS collisions from legal phrasing
and not strings.icontains(body.current_thread.text, "terms of service")
// 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
)
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