### ImpactThe 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 a server-side forgery request. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.### PatchesIf you rely on XStream's default blacklist of the [Security Framework](https://x-stream.github.io/security.html#framework), you will have to use at least version 1.4.16### WorkaroundsSee [workarounds](https://x-stream.github.io/security.html#workaround) for the different versions covering all CVEs.### ReferencesSee full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for [CVE-2021-21342](https://x-stream.github.io/CVE-2021-21342.html).### Credits钟潦贵 (Liaogui Zhong) found and reported the issue to XStream and provided the required information to reproduce it.### For more informationIf you have any questions or comments about this advisory:* Open an issue in [XStream](https://github.com/x-stream/xstream/issues)* Contact us at [XStream Google Group](https://groups.google.com/group/xstream-user)