CVE-2021-29505 (Important severity, published 2021-05-13)
CVSS score: 7.5 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H)
CWE: CWE-502
Description: A flaw was found in XStream. By manipulating the processed input stream, a remote attacker may be able to obtain sufficient rights to execute commands. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
Statement: OpenShift Container Platform (OCP) delivers Jenkins LTS package with bundled XStream library. Due to JEP-200 [1] and JEP-228 [2] Jenkins projects, OCP Jenkins package is not affected by this flaw.

CodeReady Studio 12 ships a version of xstream that is affected by this flaw as a transitive dependency for the Wise framework plugin. However, the vulnerable code is not called, so this flaw has been marked as Low severity for CodeReady Studio 12.

[1] https://github.com/jenkinsci/jep/blob/master/jep/200/README.adoc
[2] https://github.com/jenkinsci/jep/blob/master/jep/228/README.adoc#security
Mitigation: Depending on the version of XStream used there are various usage patterns that mitigate this flaw, though we would strongly recommend using the allow list approach if at all possible as there are likely more class combinations the deny list approach may not address.

Allow list approach
```java
XStream xstream = new XStream();
XStream.setupDefaultSecurity(xstream);
xstream.allowTypesByWildcard(new String[] {"com.misc.classname"})
```
Deny list for XStream 1.4.16 (this should also address some previous flaws found in 1.4.7 - > 1.4.15) 
```java
xstream.denyTypesByRegExp(new String[]{ ".*\\.Lazy(?:Search)?Enumeration.*", "(?:java|sun)\\.rmi\\..*" });
```

Deny list for XStream 1.4.15
```java
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 );
```

Deny list for XStream 1.4.13
```java
xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class });
```

Deny list for XStream 1.4.7 -> 1.4.12
```java
xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class, java.beans.EventHandler.class, java.lang.ProcessBuilder.class, java.lang.Void.class, void.class });
```

Deny list for versions prior to XStream 1.4.7
```java
xstream.registerConverter(new Converter() {
  public boolean canConvert(Class type) {
    return type != null && (type == java.beans.EventHandler.class || type == java.lang.ProcessBuilder.class || type == java.lang.Void.class || void.class || type.getName().equals("javax.imageio.ImageIO$ContainsFilter") || Proxy.isProxy(type));
  }

  public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
    throw new ConversionException("Unsupported type due to security reasons.");
  }

  public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
    throw new ConversionException("Unsupported type due to security reasons.");
  }
}, XStream.PRIORITY_LOW);
```