The account validation endpoint /v1/User/validate returns comprehensive user profile data sheets, which can be crawled by iterating predictable identification strings.
Exploitability
AV:NAC:LAT:NPR:NUI:NVulnerable System
VC:HVI:NVA:NSubsequent System
SC:NSI:NSA:N8.7/CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:NOther