diff --git a/src/main/java/com/docus/server/collection/util/XmlUtil.java b/src/main/java/com/docus/server/collection/util/XmlUtil.java
index a10dcef..17f60ce 100644
--- a/src/main/java/com/docus/server/collection/util/XmlUtil.java
+++ b/src/main/java/com/docus/server/collection/util/XmlUtil.java
@@ -245,7 +245,11 @@ public class XmlUtil {
 	private static DocumentBuilderFactory getDocumentBuilderFactory() throws ParserConfigurationException {
 		DocumentBuilderFactory dbf = XmlHelperHolder.documentBuilderFactory;
 		if (!preventedXXE) {
-			preventXXE(dbf);
+			synchronized (XmlUtil.class) {
+				if (!preventedXXE) {
+					preventXXE(dbf);
+				}
+			}
 		}
 		return dbf;
 	}
diff --git a/src/main/java/com/docus/server/report/util/XmlUtil.java b/src/main/java/com/docus/server/report/util/XmlUtil.java
index e199e2e..6402465 100644
--- a/src/main/java/com/docus/server/report/util/XmlUtil.java
+++ b/src/main/java/com/docus/server/report/util/XmlUtil.java
@@ -19,7 +19,10 @@ package com.docus.server.report.util;
 import com.docus.core.util.Exceptions;
 import com.docus.core.util.IoUtil;
 import org.springframework.lang.Nullable;
-import org.w3c.dom.*;
+import org.w3c.dom.Document;
+import org.w3c.dom.Element;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
 import org.xml.sax.InputSource;
 import org.xml.sax.SAXException;
 
@@ -245,7 +248,11 @@ public class XmlUtil {
 	private static DocumentBuilderFactory getDocumentBuilderFactory() throws ParserConfigurationException {
 		DocumentBuilderFactory dbf = XmlHelperHolder.documentBuilderFactory;
 		if (!preventedXXE) {
-			preventXXE(dbf);
+			synchronized (XmlUtil.class) {
+				if (!preventedXXE) {
+					preventXXE(dbf);
+				}
+			}
 		}
 		return dbf;
 	}