New Rule: BEC/Fraud: PenPal Scam

detection-rules/bec_fraud_penpal_scam.yml

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+name: "PenPal Scam"
+description: "This rule detects messages from individuals looking to establish contact under the guise of seeking friendship or a penpal relationship. Over time, they build trust and then exploit this relationship by asking for money, personal information, or involvement in suspicious activities."
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+
+  // the sender or the reply-to is a freemail provider
+  and (
+    sender.email.domain.domain in $free_email_providers
+    or any(headers.reply_to,
+           .email.domain.root_domain in $free_email_providers
+           and not sender.email.domain.root_domain in $free_email_providers
+    )
+  )
+
+  // body contains pen ?pal
+  and regex.contains(body.current_thread.text, 'pen\s?pal')
+
+  // and NLU Request
+  and any(ml.nlu_classifier(body.current_thread.text).entities,
+          .name == "request"
+  )
+
+  // not a reply
+  and (
+    length(headers.references) == 0
+    or not any(headers.hops, any(.fields, strings.ilike(.name, "In-Reply-To")))
+  )
+
+  // new sender
+  and (
+    (
+      profile.by_sender().prevalence in ("new", "outlier")
+      and not profile.by_sender().solicited
+    )
+    or profile.by_sender().any_messages_malicious_or_spam
+  )
+  and not profile.by_sender().any_false_positives
+
+  // negate highly trusted sender domains unless they fail DMARC authentication
+  and (
+    (
+      sender.email.domain.root_domain in $high_trust_sender_root_domains
+      and (
+        any(distinct(headers.hops, .authentication_results.dmarc is not null),
+            strings.ilike(.authentication_results.dmarc, "*fail")
+        )
+      )
+    )
+    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
+  )
+
+attack_types:
+  - "BEC/Fraud"
+tactics_and_techniques:
+  - "Free email provider"
+  - "Social engineering"
+detection_methods:
+  - "Content analysis"
+  - "Header analysis"
+  - "Sender analysis"
+id: "a4bdfa17-7527-5ee2-a27b-44d03e190773"