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.
Published: 2026-09-21
Score: 6.8 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Mon, 21 Sep 2026 20:00:00 +0000

Type Values Removed Values Added
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.
Title @sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`
Weaknesses CWE-307
References
Metrics cvssV3_1

{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-21T19:50:14.539Z

Reserved: 2026-06-29T21:54:30.332Z

Link: CVE-2026-58271

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-21T20:17:26.993

Modified: 2026-09-21T20:17:26.993

Link: CVE-2026-58271

cve-icon Redhat

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cve-icon OpenCVE Enrichment

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Weaknesses
  • CWE-307

    Improper Restriction of Excessive Authentication Attempts