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core/CHANGELOG.txt

+Drupal 8.2.8, 2017-04-19
+------------------------
+- Fixed security issues. See SA-CORE-2017-002.
+
 Drupal 8.2.7, 2017-03-15
 ------------------------
 - Fixed security issues. See SA-CORE-2017-001.

core/lib/Drupal/Core/Entity/EntityAccessControlHandler.php

@@ -303,6 +303,19 @@ public function fieldAccess($operation, FieldDefinitionInterface $field_definiti
     // Get the default access restriction that lives within this field.
     $default = $items ? $items->defaultAccess($operation, $account) : AccessResult::allowed();
 
+    // Explicitly disallow changing the entity ID and entity UUID.
+    if ($operation === 'edit') {
+      if ($field_definition->getName() === $this->entityType->getKey('id')) {
+        return $return_as_object ? AccessResult::forbidden('The entity ID cannot be changed') : FALSE;
+      }
+      elseif ($field_definition->getName() === $this->entityType->getKey('uuid')) {
+        // UUIDs can be set when creating an entity.
+        if ($items && ($entity = $items->getEntity()) && !$entity->isNew()) {
+          return $return_as_object ? AccessResult::forbidden('The entity UUID cannot be changed')->addCacheableDependency($entity) : FALSE;
+        }
+      }
+    }
+
     // Get the default access restriction as specified by the access control
     // handler.
     $entity_default = $this->checkFieldAccess($operation, $field_definition, $account, $items);