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Apache Struts 2 Documentation
S2-052
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## Summary

Possible Remote Code Execution attack when using the Struts REST plugin with XStream handler to handle XML payloads

Who should read this | All Struts 2 developers and users
Impact of vulnerability | A RCE attack is possible when using the Struts REST plugin with XStream handler to deserialise XML requests
Maximum security rating | Critical
Recommendation | Upgrade to Struts 2.5.13
Affected Software | Struts 2.5 - Struts 2.5.12
Reporter | Man Yue Mo <mmo at semmle dot com> (lgtm.com / Semmle). More information on the lgtm.com blog: https://lgtm.com/blog
CVE Identifier | CVE-2017-9805

## Problem

The REST Plugin is using a `XStreamHandler` with an instance of XStream for deserialization without any type filtering and this can lead to Remote Code Execution when deserializing XML payloads.

Solution

Upgrade to Apache Struts version 2.5.13.

## Backward compatibility

It is possible that some REST actions stop working because of applied default restrictions on available classes. In such case please investigate the new interfaces that was introduced to allow define class restrictions per action, those interfaces are:

- `org.apache.struts2.rest.handler.AllowedClasses`
- `org.apache.struts2.rest.handler.AllowedClassNames`
- `org.apache.struts2.rest.handler.XStreamPermissionProvider`

## Workaround

No workaround is possible, the best option is to remove the Struts REST plugin when not used or limit it to server normal pages and JSONs only:

    <constant name="struts.action.extension" value="xhtml,,json" />