Username timing attack on recover password/MFA token in vantage6

Vulnerability Description

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.

References

• https://github.com/vantage6/vantage6/security/advisories/GHSA-5h3x-6gwf-73jm
• https://github.com/vantage6/vantage6/security/advisories/GHSA-45gq-q4xh-cp53
• https://github.com/vantage6/vantage6/commit/aecfd6d0e83165a41a60ebd52d2287b0217be26b