XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability where the 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. If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16.
Exploitability
AV:NAC:HPR:NUI:RScope
S:UImpact
C:NI:HA:N5.3/CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:NInput Validation
Serialization