Affected versions of Atlassian Jira Server and Data Center allow remote attackers to inject arbitrary HTML or JavaScript via a Reflected Cross-Site Scripting (XSS) vulnerability in the /rest/collectors/1.0/template/custom endpoint. To exploit this issue the attacker must trick a user into visiting a malicious website. The affected versions are before version 8.13.15 and from version 8.14.0 before 8.20.3.