The "have you forgotten your password" links in the User module in Drupal 7.x before 7.43 and 8.x before 8.0.4 allow remote attackers to obtain sensitive username information by leveraging a configuration that permits using an email address to login and a module that permits logging in.

References

• https://nvd.nist.gov/vuln/detail/CVE-2016-3170
• https://www.drupal.org/SA-CORE-2016-001
• http://www.debian.org/security/2016/dsa-3498
• http://www.openwall.com/lists/oss-security/2016/02/24/19
• http://www.openwall.com/lists/oss-security/2016/03/15/10
• https://github.com/FriendsOfPHP/security-advisories/blob/master/drupal/core/CVE-2016-3170.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/drupal/drupal/CVE-2016-3170.yaml