Create bec_urgent_suspicious_patterns.yml

detection-rules/bec_urgent_suspicious_patterns.yml

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+name: "BEC/Fraud: Urgent Language and Suspicious Sending/Infrastructure Patterns"
+description: "Identifies inbound messages using urgent language patterns and sender behavioral traits common in social manipulation. Combines multiple indicators including urgent subject lines, characteristic message content, short message length, and suspicious sender attributes."
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+
+  and 3 of (
+    // urgent subjects
+    strings.ilike(subject.subject, '*quick question*'),
+    strings.ilike(subject.subject, '*urgent*request*'),
+    strings.ilike(subject.subject, '*are you available*'),
+    strings.ilike(subject.subject, '*need assistance*'),
+    strings.ilike(subject.subject, '*help*needed*'),
+
+    // BEC body patterns
+    strings.ilike(body.current_thread.text, '*sorry to bother*'),
+    strings.ilike(body.current_thread.text, '*are you busy*'),
+    strings.ilike(body.current_thread.text, '*can you help*'),
+    strings.ilike(body.current_thread.text, '*do you have a moment*'),
+    strings.ilike(body.current_thread.text, '*please respond*asap*'),
+
+    // brand name
+    strings.ilike(body.current_thread.text, '*amaz*n*'), // Catches "Amaz on", "Amazon", etc.
+    strings.ilike(body.current_thread.text, '*pay*pal*'),
+    strings.ilike(body.current_thread.text, '*app*le*'),
+
+    // short body
+    length(body.current_thread.text) < 200,
+    strings.count(body.current_thread.text, ' ') < 30
+  )
+
+  and 3 of (
+    // suspicious sender
+    sender.email.domain.root_domain in $free_email_providers,
+    network.whois(sender.email.domain).days_old < 30,
+
+    // suspicious recipient pattern
+    any(recipients.to, strings.ilike(.display_name, 'undisclosed?recipients')),
+    length(recipients.to) == 1, // Single recipient
+
+    // header checks
+    strings.starts_with(headers.mailer, 'Open-Xchange Mailer'),
+    strings.ilike(headers.x_originating_ip.ip, '*.*.*.0'), // Common in some BEC campaigns
+  )
+  and profile.by_sender_email().prevalence not in ("common")
+
+attack_types:
+  - "BEC/Fraud"
+  - "Callback Phishing"
+  - "Spam"
+tactics_and_techniques:
+  - "Impersonation: Brand"
+  - "Social engineering"
+  - "Free email provider"
+detection_methods:
+  - "Content analysis"
+  - "Header analysis"
+  - "Sender analysis"
+  - "Whois"
+id: "ba8a79e0-cce3-57e8-bbc7-3b3d9f848761"