diff --git a/manager/src/main/java/org/apache/hertzbeat/manager/service/impl/MailServiceImpl.java b/manager/src/main/java/org/apache/hertzbeat/manager/service/impl/MailServiceImpl.java
index 4e91ea73d6f..ec627f81548 100644
--- a/manager/src/main/java/org/apache/hertzbeat/manager/service/impl/MailServiceImpl.java
+++ b/manager/src/main/java/org/apache/hertzbeat/manager/service/impl/MailServiceImpl.java
@@ -18,6 +18,7 @@
 package org.apache.hertzbeat.manager.service.impl;
 
 import freemarker.cache.StringTemplateLoader;
+import freemarker.core.TemplateClassResolver;
 import freemarker.template.Configuration;
 import freemarker.template.TemplateException;
 import java.io.IOException;
@@ -99,6 +100,7 @@ public String buildAlertHtmlTemplate(final Alert alert, NoticeTemplate noticeTem
         String templateName = "mailTemplate";
         stringLoader.putTemplate(templateName, noticeTemplate.getContent());
         cfg.setTemplateLoader(stringLoader);
+        cfg.setNewBuiltinClassResolver(TemplateClassResolver.SAFER_RESOLVER);
         templateMail = cfg.getTemplate(templateName, Locale.CHINESE);
         return FreeMarkerTemplateUtils.processTemplateIntoString(templateMail, model);
     }