Create link_zoho_forms_unsolicited.yml

detection-rules/link_zoho_forms_unsolicited.yml

@@ -0,0 +1,68 @@
+name: "Link: Zoho Form Link from Unsolicited Sender"
+description: "This detection rule matches on messages containing at least one link to forms.zohopublic.com from an unsolicited sender. Zoho provides a free plan enabling users to create custom websites and file hosting. This service has been abused by threat actors to host landing pages via forms directing victims to a next stage of credential phishing."
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+  // filter links to zoho forms
+  and any(filter(body.links,
+                 // zoho forms link
+                 .href_url.domain.domain == 'forms.zohopublic.com'
+                 // remove a common FP for linking directly 
+                 and not strings.istarts_with(.href_url.path, '/quickbooking/')
+          ),
+          // remove FPs by checking there is only one link
+          // ensure the link is within the current_thread
+          (
+            strings.contains(body.current_thread.text, .display_text)
+            or strings.contains(body.current_thread.text, .href_url.url)
+          )
+          // and ensure that link only occurs once within body.html
+          and (
+            (
+              body.html.raw is not null
+              and (
+                strings.count(body.html.raw, .display_text) == 1
+                or strings.count(body.html.raw, .href_url.url) == 1
+              )
+            )
+            or (
+              // and ensure that link only occurs once within plaintext if html.raw is null
+              body.plain.raw is not null
+              and (
+                strings.count(body.plain.raw, .display_text) == 1
+                or strings.count(body.plain.raw, .href_url.url) == 1
+              )
+            )
+          )
+  )
+
+  // dont match messages with lots of links or long bodies, often marketing messages
+  and length(body.links) < 20
+  and length(body.current_thread.text) < 900
+  // not solicited or from malicious/spam user with no FPs
+  and (
+    not profile.by_sender().solicited
+    or (
+      profile.by_sender().any_messages_malicious_or_spam
+      and not profile.by_sender().any_false_positives
+    )
+  )
+
+  // 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:
+  - "Callback Phishing"
+tactics_and_techniques:
+  - "Free file host"
+detection_methods:
+  - "Content analysis"
+  - "URL analysis"
+  - "Sender analysis"
+id: "eb04a9f2-c40b-5fcc-97de-bee7111bc3d8"