URL Redirection to Untrusted Site ('Open Redirect')
An issue was discovered in Mattermost Server before 4.2.0, 4.1.1, and 4.0.5. It allows Phishing because an error page can have a link.
CWE-601 - Open Redirect
An open redirect attack employs a URL parameter, HTML refresh tags, or a DOM based location change to exploit the trust of a vulnerable domain to direct the users to a malicious website. The attack could lead to higher severity vulnerabilities such as unauthorized access control, account takeover, XSS, and more.