--- a/src/java.base/share/classes/java/net/NetPermission.java	Mon Oct 07 17:12:22 2019 +0200
+++ b/src/java.base/share/classes/java/net/NetPermission.java	Mon Mar 25 17:15:27 2019 +0000
@@ -145,6 +145,15 @@
  *   </tr>
  *
  * <tr>
+ *   <th scope="row">setSocketImpl</th>
+ *   <td>The ability to create a sub-class of Socket or ServerSocket with a
+ *   user specified SocketImpl.</td>
+ *   <td>Malicious user-defined SocketImpls can change the behavior of
+ *   Socket and ServerSocket in surprising ways, by virtue of their
+ *   ability to access the protected fields of SocketImpl.</td>
+ *   </tr>
+ *
+ * <tr>
  *   <th scope="row">specifyStreamHandler</th>
  *   <td>The ability
  *   to specify a stream handler when constructing a URL</td>

--- a/src/java.base/share/classes/java/net/ServerSocket.java	Mon Oct 07 17:12:22 2019 +0200
+++ b/src/java.base/share/classes/java/net/ServerSocket.java	Mon Mar 25 17:15:27 2019 +0000
@@ -32,6 +32,7 @@
 import java.util.Set;
 import java.util.Collections;
 
+import sun.security.util.SecurityConstants;
 import sun.net.PlatformSocketImpl;
 
 /**
@@ -73,13 +74,25 @@
      *
      * @throws     NullPointerException if impl is {@code null}.
      *
+     * @throws     SecurityException if a security manager is set and
+     *             its {@code checkPermission} method doesn't allow
+     *             {@code NetPermission("setSocketImpl")}.
      * @since 12
      */
     protected ServerSocket(SocketImpl impl) {
         Objects.requireNonNull(impl);
+        checkPermission();
         this.impl = impl;
     }
 
+    private static Void checkPermission() {
+        SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            sm.checkPermission(SecurityConstants.SET_SOCKETIMPL_PERMISSION);
+        }
+        return null;
+    }
+
     /**
      * Creates an unbound server socket.
      *

--- a/src/java.base/share/classes/java/net/Socket.java	Mon Oct 07 17:12:22 2019 +0200
+++ b/src/java.base/share/classes/java/net/Socket.java	Mon Mar 25 17:15:27 2019 +0000
@@ -25,6 +25,8 @@
 
 package java.net;
 
+import sun.security.util.SecurityConstants;
+
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.IOException;
@@ -182,12 +184,28 @@
      *
      * @throws    SocketException if there is an error in the underlying protocol,
      * such as a TCP error.
+     *
+     * @throws SecurityException if {@code impl} is non-null and a security manager is set
+     * and its {@code checkPermission} method doesn't allow {@code NetPermission("setSocketImpl")}.
+     *
      * @since   1.1
      */
     protected Socket(SocketImpl impl) throws SocketException {
+        checkPermission(impl);
         this.impl = impl;
     }
 
+    private static Void checkPermission(SocketImpl impl) {
+        if (impl == null) {
+            return null;
+        }
+        SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            sm.checkPermission(SecurityConstants.SET_SOCKETIMPL_PERMISSION);
+        }
+        return null;
+    }
+
     /**
      * Creates a stream socket and connects it to the specified port
      * number on the named host.

--- a/src/java.base/share/classes/sun/security/util/SecurityConstants.java	Mon Oct 07 17:12:22 2019 +0200
+++ b/src/java.base/share/classes/sun/security/util/SecurityConstants.java	Mon Mar 25 17:15:27 2019 +0000
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -97,6 +97,10 @@
     public static final NetPermission GET_RESPONSECACHE_PERMISSION =
        new NetPermission("getResponseCache");
 
+    // java.net.ServerSocket, java.net.Socket
+    public static final NetPermission SET_SOCKETIMPL_PERMISSION =
+        new NetPermission("setSocketImpl");
+
     // java.lang.SecurityManager, sun.applet.AppletPanel
     public static final RuntimePermission CREATE_CLASSLOADER_PERMISSION =
         new RuntimePermission("createClassLoader");