CVE-2026-58271 @sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`
Attackers can brute-force TOTP codes to register sync clients and disable MFA, leading to account takeover.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-58271?
CVE-2026-58271 is a medium-severity authentication bypass vulnerability in Sync-in server, published on 21 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
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.
Weakness: CWE-307
Which versions are affected by CVE-2026-58271?
2 open source packages ship an affected version, including @sync-in/server.
| Package | Affected | Fixed in |
|---|---|---|
@sync-in/server npm | All versions | 2.4.0 |
@sync-in/server npm | All versions | 2.4.0 |
How do I fix CVE-2026-58271?
Upgrade @sync-in/server to 2.4.0 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-58271 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-58271 exists.
Sources
Also known as GHSA-274f-6w77-8qm9.