XStream before 1.4.18 is susceptible to server-side request forgery. An attacker can request data from internal resources that are not publicly available by manipulating the processed input stream with a Java runtime version 14 to 8. This makes it possible to obtain sensitive information, modify data, and/or execute unauthorized administrative operations in the context of the affected site.
View the template here CVE-2021-39152.yaml
References:
https://nvd.nist.gov/vuln/detail/cve-2021-39152