CVE-2019-14831
A vulnerability was found in Moodle 3.7 to 3.7.1, 3.6 to 3.6.5, 3.5 to 3.5.7 and earlier unsupported versions, where forum subscribe link contained an open redirect if forced subscription mode was enabled. If a forum’s subscription mode was set to "forced subscription", the forum’s subscribe link contained an open redirect.
Source: CVE-2019-14831