Inside a Jira instance any user (even non-authenticated) can check its privileges in
/rest/api/3/mypermissions. These endpoints will return your current privileges. If a non-authenticated user have any privilege, this is a vulnerability (bounty?). If an authenticated user have any unexpected privilege, this a a vuln.
#Check non-authenticated privileges
curl https://jira.some.example.com/rest/api/2/mypermissions | jq | grep -iB6 '"havePermission": true'