Jira before 8.4.0 is susceptible to information disclosure. The /rest/api/latest/groupuserpicker resource can allow an attacker to enumerate usernames, and thereby potentially obtain sensitive information, modify data, and/or execute unauthorized operations.
View the template here CVE-2019-8449.yaml
References:
https://nvd.nist.gov/vuln/detail/CVE-2019-8449