CVE-2021-26081

REST API in Atlassian Jira Server and Jira Data Center before version 8.5.14, from version 8.6.0 before 8.13.6, and from version 8.14.0 before 8.16.1 allows remote attackers to enumerate usernames via a Sensitive Data Exposure vulnerability in the `/rest/api/latest/user/avatar/temporary` endpoint.

Source: CVE-2021-26081