vantage6 is an open source framework built to enable, manage and deploy privacy enhancing technologies like Federated Learning and Multi-Party Computation. Much like GHSA-45gq-q4xh-cp53, it is possible to find which usernames exist in vantage6 by calling the API routes /recover/lost and /2fa/lost. These routes send emails to users if they have lost their password or MFA token. This issue has been addressed in commit aecfd6d0e and is expected to ship in subsequent releases. Users are advised to upgrade as soon as a new release is available. There are no known workarounds for this vulnerability.
Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.