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CVE-2026-58271— @sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`

Quick assessment

Affected
Sync-in server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Sync-in Server is an open-source platform for file storage, sharing, collaboration, and syncing. Prior to version 2.4.0, accepts credentials and a TOTP code to register a desktop sync client. On a failed TOTP, calls , which hits a freeze branch that writes bac

CVSS 6.8 · Medium EPSS 0.18% · P8
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I. Basic Information for CVE-2026-58271

Vulnerability Information

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Vulnerability Title
@sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
过多认证尝试的限制不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Sync-in server < 2.4.0 -

II. Public POCs for CVE-2026-58271

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III. Intelligence Information for CVE-2026-58271

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Other References for CVE-2026-58271 (1)

Same Patch Batch · Sync-in · 2026-09-21 · 4 CVEs total

CVE-2026-58269 8.1 HIGH Sync-in Server has a complete 2FA Bypass via `POST /api/auth/token`
CVE-2026-58270 6.5 MEDIUM Sync-in Server has a ReDoS via Unsanitized Regex in Sync Diff `pathFilters`
CVE-2026-58272 5.3 MEDIUM Sync-in Server has Username/Login Enumeration via Timing Side-Channel on POST /api/auth/lo

IV. Related Vulnerabilities

Same product: server
Same vendor: Sync-in
Same weakness: CWE-307

V. Comments for CVE-2026-58271

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