Mattermost versions 10.11.x <= 10.11.4 fail to validate redirect URLs on the /error page, which allows an attacker to redirect a victim to a malicious site via a crafted link opened in a new tab.
Exploitability
AV:NAC:HPR:NUI:RScope
S:UImpact
C:NI:LA:N3.1/CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:NInput Validation