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CVE-2021-39139.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<!--
Copyright (C) 2005, 2006 Joe Walnes.
Copyright (C) 2006, 2007, 2008, 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 29. January 2005 by Joe Walnes
-->
<head>
<title>XStream - CVE-2021-39139</title>
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<h1 class="FirstChild">CVE-2021-39139</h1>
<h2 id="vulnerability">Vulnerability</h2>
<p>CVE-2021-39139: XStream is vulnerable to an Arbitrary Code Execution attack.</p>
<h2 id="affected_versions">Affected Versions</h2>
<p>All versions until and including version 1.4.17 are affected, if using the version out of the box with JDK
1.7u21 or below. However, this scenario can be adjusted easily to an external Xalan that works regardless of the
version of the Java runtime. 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 arbitrary code loaded from a remote server.</p>
<h2 id="reproduction">Steps to Reproduce</h2>
<p>Create a simple LinkedHashSet and use XStream to marshal it to XML. Replace the XML with following snippet and
unmarshal it again with XStream:</p>
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</pre></div>
<div class="Source Java"><pre>XStream xstream = new XStream();
xstream.fromXML(xml);
</pre></div>
<p>Depending on the JDK, the code from the remote server is executed as soon as the XML gets unmarshalled.</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 to execute arbitrary code 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>Lai Han of nsfocus security team found and reported the issue to XStream and provided the required information to reproduce it.</p>
<br/>
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