### ImpactThe vulnerability may allow a remote attacker to allocate 100% CPU time on the target system depending on CPU type or parallel execution of such a payload resulting in a denial of service only by manipulating the processed input stream. 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-2021-39140](https://x-stream.github.io/CVE-2021-39140.html).### CreditsThe vulnerability was discovered and reported by Lai Han of nsfocus security team.### 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)