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.
Weakness
The product does not implement sufficient measures to prevent multiple failed authentication attempts within a short time frame.
Potential Mitigations
Common protection mechanisms include:
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
Consider using libraries with authentication capabilities such as OpenSSL or the ESAPI Authenticator. [REF-45]
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/16.html
- https://cwe.mitre.org/data/definitions/49.html
- https://cwe.mitre.org/data/definitions/560.html
- https://cwe.mitre.org/data/definitions/565.html
- https://cwe.mitre.org/data/definitions/600.html
- https://cwe.mitre.org/data/definitions/652.html
- https://cwe.mitre.org/data/definitions/653.html