### ImpactThe vulnerability may allow a remote attacker to load and execute arbitrary code from a remote host only by manipulating the processed input stream. A user is only affected if using the version out of the box with JDK 1.7u21 or below. However, this scenario can be adjusted easily to an external Xalan that works regardless of the version of the Java runtime. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.### PatchesXStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.### 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-2021-39139](https://x-stream.github.io/CVE-2021-39139.html).### CreditsLai Han of nsfocus security team 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)