[PR #3740] added rule: Cloud storage impersonation with credential theft indicators

Author: github-actions[bot]

detection-rules/3740_credential_theft_cloud_storage_impersonation.yml

@@ -0,0 +1,79 @@
+name: "Cloud storage impersonation with credential theft indicators"
+description: "Detects messages impersonating cloud storage services that contain hyperlinked images leading to free file hosts, where message screenshots reveal high-confidence credential theft language and storage-related urgency tactics."
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+  and 0 < length(body.current_thread.links) < 8
+  and any([subject.subject, sender.display_name],
+          regex.icontains(., "(?:cloud|storage|mailbox)")
+  )
+  and any(ml.nlu_classifier(beta.ocr(file.message_screenshot()).text).intents,
+          .name == "cred_theft" and .confidence == "high"
+  )
+  and regex.icontains(beta.ocr(file.message_screenshot()).text,
+                      "storage.{0,50}full",
+                      "free.{0,50}upgrade",
+                      "storage.{0,50}details",
+                      "storage.{0,50}quot",
+                      "(?:mailbox|cloud|account).{0,50}disabled",
+                      "(?:email|cloud|total).{0,50}storage",
+                      "(?:account|cloud).{0,50}(?:suspended?|at risk)"
+  )
+  and not strings.ilike(beta.ocr(file.message_screenshot()).text, "*free plan*")
+  and (
+    any(body.current_thread.links,
+        // fingerprints of a hyperlinked image
+        .display_text is null
+        and .display_url.url is null
+        and .href_url.domain.domain not in $tenant_domains
+        and (
+          .href_url.domain.root_domain in $free_file_hosts
+          or .href_url.domain.root_domain == "beehiiv.com"
+        )
+    )
+    or (
+      (
+        not headers.auth_summary.spf.pass
+        or (
+          headers.return_path.domain.root_domain is not null
+          and headers.return_path.domain.root_domain != sender.email.domain.root_domain
+        )
+      )
+      // negate security training platforms
+      and headers.return_path.domain.root_domain not in~ (
+        "knowbe4.com",
+        "proofpoint.com",
+        "cofense.com",
+        "infosec.com"
+      )
+    )
+  )
+  
+  // and the sender is not from high trust sender root domains
+  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:
+  - "Credential Phishing"
+tactics_and_techniques:
+  - "Free file host"
+  - "Image as content"
+  - "Impersonation: Brand"
+  - "Social engineering"
+detection_methods:
+  - "Computer Vision"
+  - "Content analysis"
+  - "Header analysis"
+  - "Natural Language Understanding"
+  - "Optical Character Recognition"
+  - "Sender analysis"
+  - "URL analysis"
+id: "6e9cade3-a304-5f94-83af-3cd1cbadea90"
+og_id: "4c20f72c-0045-518c-8157-7dad5f196ecc"
+testing_pr: 3740
+testing_sha: a91481c8a3f4ad2a12178718757ba8b66dabbbd9