Passbolt API before 5, if the server is misconfigured (with an incorrect installation process and disregarding of Health Check results), can send email messages with a domain name taken from an attacker-controlled HTTP Host header.
Exploitability
AV:NAC:LAT:PPR:NUI:AVulnerable System
VC:NVI:LVA:NSubsequent System
SC:NSI:LSA:N2.1/CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:L/SA:NOther