diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1844,6 +1844,7 @@
     'PhabricatorFilesManagementPurgeWorkflow' => 'applications/files/management/PhabricatorFilesManagementPurgeWorkflow.php',
     'PhabricatorFilesManagementRebuildWorkflow' => 'applications/files/management/PhabricatorFilesManagementRebuildWorkflow.php',
     'PhabricatorFilesManagementWorkflow' => 'applications/files/management/PhabricatorFilesManagementWorkflow.php',
+    'PhabricatorFilesOutboundRequestAction' => 'applications/files/action/PhabricatorFilesOutboundRequestAction.php',
     'PhabricatorFlag' => 'applications/flag/storage/PhabricatorFlag.php',
     'PhabricatorFlagColor' => 'applications/flag/constants/PhabricatorFlagColor.php',
     'PhabricatorFlagConstants' => 'applications/flag/constants/PhabricatorFlagConstants.php',
@@ -5160,6 +5161,7 @@
     'PhabricatorFilesManagementPurgeWorkflow' => 'PhabricatorFilesManagementWorkflow',
     'PhabricatorFilesManagementRebuildWorkflow' => 'PhabricatorFilesManagementWorkflow',
     'PhabricatorFilesManagementWorkflow' => 'PhabricatorManagementWorkflow',
+    'PhabricatorFilesOutboundRequestAction' => 'PhabricatorSystemAction',
     'PhabricatorFlag' => array(
       'PhabricatorFlagDAO',
       'PhabricatorPolicyInterface',
diff --git a/src/applications/files/action/PhabricatorFilesOutboundRequestAction.php b/src/applications/files/action/PhabricatorFilesOutboundRequestAction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/files/action/PhabricatorFilesOutboundRequestAction.php
@@ -0,0 +1,22 @@
+<?php
+
+final class PhabricatorFilesOutboundRequestAction
+  extends PhabricatorSystemAction {
+
+  const TYPECONST = 'files.outbound';
+
+  public function getActionConstant() {
+    return self::TYPECONST;
+  }
+
+  public function getScoreThreshold() {
+    return 60 / phutil_units('1 hour in seconds');
+  }
+
+  public function getLimitExplanation() {
+    return pht(
+      'You have initiated too many outbound requests to fetch remote URIs '.
+      'recently.');
+  }
+
+}
diff --git a/src/applications/macro/controller/PhabricatorMacroEditController.php b/src/applications/macro/controller/PhabricatorMacroEditController.php
--- a/src/applications/macro/controller/PhabricatorMacroEditController.php
+++ b/src/applications/macro/controller/PhabricatorMacroEditController.php
@@ -72,6 +72,13 @@
           ));
       } else if ($uri) {
         try {
+          // Rate limit outbound fetches to make this mechanism less useful for
+          // scanning networks and ports.
+          PhabricatorSystemActionEngine::willTakeAction(
+            array($user->getPHID()),
+            new PhabricatorFilesOutboundRequestAction(),
+            1);
+
           $file = PhabricatorFile::newFromFileDownload(
             $uri,
             array(