Create francais_business_email_compromise_new_sender.yml (#2026)

Co-authored-by: ID Generator <[email protected]>

detection-rules/francais_business_email_compromise_new_sender.yml

@@ -0,0 +1,59 @@
+name: "Business Email Compromise (BEC) attempt from untrusted sender (French/Français)"
+description: "Detects potential Business Email Compromise (BEC) attacks by searching for common French BEC language within the email body from first-time senders."
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+  and length(body.links) == 0
+  and ml.nlu_classifier(body.current_thread.text).language == "french"
+  and 1 of (
+    regex.icontains(subject.subject,
+                    '(mise (a|à) jour|changé|changement).{0,20}(bancaire|de banque)'
+    ),
+    regex.icontains(body.current_thread.text,
+                    '(changement|changé) de (banque)|changement bancaire|coordonnées.{0,20}(compte|banque|bancaire|salaire)',
+    ),
+    (regex.icontains(body.current_thread.text, 'parler.{0,20}confiance'))
+  )
+  // negating legit replies
+  and not (
+    (
+      strings.istarts_with(subject.subject, "RE:")
+      // out of office auto-reply
+      // the NLU model will handle these better natively soon
+      or strings.istarts_with(subject.subject, "Automatic reply:")
+      or regex.imatch(subject.subject,
+                      '(\[[^\]]+\]\s?){0,3}(re|fwd?|automat.*)\s?:.*'
+      )
+    )
+    and (
+      length(headers.references) > 0
+      or any(headers.hops, any(.fields, strings.ilike(.name, "In-Reply-To")))
+    )
+  )
+  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 not headers.auth_summary.dmarc.pass
+    )
+    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
+  )
+
+attack_types:
+  - "BEC/Fraud"
+tactics_and_techniques:
+  - "Social engineering"
+detection_methods:
+  - "Content analysis"
+  - "Header analysis"
+  - "Sender analysis"
+id: "b7d1e096-d9cc-5a79-9753-5d9565794433"