Sync from PR#992

New rule - Brand impersonation: Sharepoint fake file share by @jkamdjou
#992
Source SHA 28da4a6
Triggered by @jkamdjou

detection-rules/impersonation_sharepoint_fake_file_share.yml

@@ -0,0 +1,67 @@
+name: "Brand impersonation: Sharepoint fake file share"
+description: |
+  This rule detects messages impersonating a Sharepoint file sharing email where no links point to known Microsoft domains.
+type: "rule"
+severity: "medium"
+source: |
+  type.inbound
+
+  // Sharepoint body content looks like this
+  and strings.contains(body.current_thread.text, "shared a file with you")
+  and strings.icontains(subject.subject, "shared")
+  and any(ml.logo_detect(beta.message_screenshot()).brands, .name == "Microsoft")
+
+  // fake Sharepoint shares are easy to identify if there are any links
+  // that don't point to microsoft[.]com or *.sharepoint[.]com
+  and not all(body.links,
+              .href_url.domain.root_domain in ("microsoft.com", "sharepoint.com")
+  )
+  and sender.email.domain.root_domain not in $org_domains
+  and sender.email.domain.root_domain not in (
+    "bing.com",
+    "microsoft.com",
+    "microsoftonline.com",
+    "microsoftsupport.com",
+    "microsoft365.com",
+    "office.com",
+    "onedrive.com",
+    "sharepointonline.com",
+    "yammer.com"
+  )
+
+  // 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
+  )
+  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
+    )
+  )
+attack_types:
+  - "Credential Phishing"
+  - "Malware/Ransomware"
+detection_methods:
+  - "Content analysis"
+  - "Header analysis"
+  - "URL analysis"
+  - "Computer Vision"
+tactics_and_techniques:
+  - "Impersonation: Brand"
+  - "Social engineering"
+id: "ff8b296b-aa0d-5df0-b4d2-0e599b688f6a"
+testing_pr: 992
+testing_sha: 28da4a6f50a819b62afa785a52f6481cbbe0042e