Vulnerability · Published Sep 21, 2026 · Assigned by GitHub_M
CVE-2026-58271@sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`
Medium 6.8
In plain English
A medium-severity security flaw in server from Sync-in. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 12% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | @sync-in/server | 2.4.0 | GHSA-274f-6w77-8qm9 |
Affected products (as reported)
Weakness: CWE-307 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
References
- https://github.com/Sync-in/server/security/advisories/GHSA-274f-6w77-8qm9 x_refsource_CONFIRM