Jira < 7.13.3, 8.0.0-8.0.3, 8.1.0 - Unauthenticated Username Enumeration via User Picker REST Endpoint
The /rest/api/2/user/picker rest resource in Jira before version 7.13.3, from version 8.0.0 before version 8.0.4, and from version 8.1.0 before version 8.1.1 allows remote attackers to enumerate usernames via an incorrect authorisation check.