XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerability may allow a remote attacker has sufficient rights to execute commands of the host 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. XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.
Use CWE-94, Xstream vendor hub and Xstream product page to widen CVE-2021-39144 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2021-39152, CVE-2021-39150 and CVE-2021-39154 for nearby disclosures in the same product family.