New credential phishing rules (#995)

detection-rules/link_content_credential_phishing.yml

@@ -0,0 +1,61 @@
+name: "Credential phishing content and link (first-time sender)"
+description: |
+  Message contains credential theft language and a link to a credential phishing page from an unknown sender.
+  We use Link Analysis in aggressive mode to increase our chances of scanning.
+type: "rule"
+severity: "high"
+source: |
+  type.inbound
+  and (
+    any(ml.nlu_classifier(body.current_thread.text).intents,
+        .name == "cred_theft" and .confidence in ("medium", "high")
+    )
+    // embedded in an image attachment
+    // note: don't use message_screenshot() for now
+    // because it's not limited to current_thread and may FP
+    or any(attachments,
+           .file_type in $file_types_images
+           and any(file.explode(.),
+                   any(ml.nlu_classifier(.scan.ocr.raw).intents,
+                       .name == "cred_theft" and .confidence in ("medium", "high")
+                   )
+           )
+    )
+  )
+  and any(body.links,
+          beta.linkanalysis(., mode="aggressive").credphish.disposition == "phishing"
+          and beta.linkanalysis(., mode="aggressive").credphish.confidence in (
+            "medium",
+            "high"
+          )
+  )
+  and (
+    profile.by_sender().prevalence in ("new", "outlier")
+    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:
+  - "Credential Phishing"
+tactics_and_techniques:
+  - "Social engineering"
+detection_methods:
+  - "Computer Vision"
+  - "Sender analysis"
+  - "URL analysis"
+  - "URL screenshot"
+id: "f0c95bb7-afeb-5c8d-a654-74b5e026007f"

detection-rules/link_credential_phishing_intent_and_other_indicators_2.yml

@@ -0,0 +1,112 @@
+name: "Credential phishing language and suspicious indicators (unknown sender)"
+description: |
+  Message contains various suspicious indicators as well as engaging language resembling credential theft from an unknown sender.
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+  and (
+    any(ml.nlu_classifier(body.current_thread.text).intents,
+        .name == "cred_theft" and .confidence in ("medium", "high")
+    )
+    // embedded in an image attachment
+    // note: don't use message_screenshot()
+    // because it's not limited to current_thread and may FP
+    or any(attachments,
+           .file_type in $file_types_images
+           and any(file.explode(.),
+                   any(ml.nlu_classifier(.scan.ocr.raw).intents,
+                       .name == "cred_theft" and .confidence == "high"
+                   )
+           )
+    )
+  )
+  and 4 of (
+    // impersonation of the recipient's domain or email address
+    // in the subject to make it look more personalized
+    any(recipients.to,
+        strings.icontains(subject.subject, .email.local_part)
+        or strings.icontains(subject.subject, .email.domain.sld)
+    ),
+    // recipient's email address in the body. this is not very uncommon
+    // for legit credential themed messages either
+    any(recipients.to,
+        .email.domain.valid
+        and strings.icontains(body.current_thread.text, .email.email)
+    ),
+    (
+      // freemail providers should never be sending this type of email
+      sender.email.domain.domain in $free_email_providers
+
+      // if not freemail, it's suspicious if the sender's root domain
+      // doesn't match any links in the body
+      or (
+        length(body.links) > 0
+        and all(body.links,
+                .href_url.domain.root_domain != sender.email.domain.root_domain
+        )
+      )
+    ),
+    strings.contains(body.current_thread.text,
+                     "Your mailbox can no longer send or receive messages."
+    ),
+      // link redirects to a suspicious TLD
+      any(body.links,
+          any(beta.linkanalysis(., mode="aggressive").redirect_history, .domain.tld in $suspicious_tlds)
+    ),
+    (
+      // suspicious redirects
+      // 3 or more different domains with 2 or more different TLDs
+      // careful because click trackers will always make this at least 2
+      // different domains and not unlikely 2 or more TLDs
+      any(body.links,
+          length(distinct(map(beta.linkanalysis(., mode="aggressive").redirect_history,
+                              .domain.tld
+                          )
+                 )
+          ) >= 2
+          and length(distinct(map(beta.linkanalysis(., mode="aggressive").redirect_history,
+                                  .domain.domain
+                              )
+                     )
+          ) >= 3
+      )
+    ),
+  // maybe: any brand logo with high confidence
+  // maybe: recipients BCCd or undisclosed
+  )
+  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:
+  - "Credential Phishing"
+tactics_and_techniques:
+  - "Free email provider"
+  - "Social engineering"
+detection_methods:
+  - "Content analysis"
+  - "Header analysis"
+  - "Natural Language Understanding"
+  - "Sender analysis"
+  - "URL analysis"
+id: "89c186f7-8c8d-55db-8b6f-da6ead587b1d"