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[ CVE-2026-58271 · Published 21 Sep 2026 ]

@sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`

CVSS 6.8 EPSS <1%Fix available

[ Why it matters ]Priority signals

  • Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

Sync-in Server is an open-source platform for file storage, sharing, collaboration, and syncing. Prior to version 2.4.0, `POST /api/app/sync/register` accepts credentials and a TOTP code to register a desktop sync client. On a failed TOTP, `SyncClientsManager.register()` calls `updateAccesses(user, ip, false)`, which hits a freeze branch that writes `passwordAttempts` back unchanged. The counter never reaches `USER_MAX_PASSWORD_ATTEMPTS` (10) and the lockout gate never fires. A successful guess returns a `{clientId, clientToken}` pair. The token can be exchanged via `POST /api/app/sync/auth/cookie` for a full JWT. While the code is valid, the attacker can also call `POST /api/auth/2fa/disable` to permanently remove MFA. Version 2.4.0 patches the issue.

[ Fixes ]Fixes and patches

  • @sync-in/server 2.4.0Fixed version · GitHub Advisories · npm package @sync-in/server: upgrade to 2.4.0 or later (affected <= 2.3.0)

[ Packages ]Affected open-source packages

[ References ]References