XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerability may allow a remote attacker to request data from internal resources that are not publicly available only by manipulating the processed input stream with a Java runtime version 14 to 8. 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 1.4.18.
Exploitability
AV:NAC:HPR:LUI:NScope
S:CImpact
C:HI:HA:H8.5/CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:HInput Validation
Serialization