Capgo before 12.128.12 allows authenticated users to modify their mutable public.users.email to arbitrary addresses, which the SSO provisioning endpoint trusts as an account-merge key. Attackers can pre-position their account with a victim's corporate SSO email, causing the provision-user endpoint to merge the victim's SSO identity into the attacker-controlled account.
https://github.com/Cap-go/capgo/security/advisories/GHSA-wqc6-fhwf-qpww