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CVE-2026-58271

6.8 MEDIUMpublic exploit available

Published 2026-09-21 · Updated 2026-09-21

AI risk analysis

Summary
The flaw allows an attacker to bypass multi-factor authentication (MFA) and gain full access by successfully guessing a TOTP code or directly disabling MFA.
Exploitability
Exploitation requires guessing a TOTP code, which is moderately hard due to the nature of time-based one-time passwords. Precondition: Access to the `/api/app/sync/register` endpoint.
Blast radius
If exploited, this could lead to unauthorized access and full control over user accounts, potentially compromising sensitive data.
Prioritized remediation
Upgrade to Sync-in Server version 2.4.0 or later to apply the necessary security patches.
auth-bypassmfaapi-exploitjwt

Analysis generated locally by qwen2.5:7b-instruct (no data left the box). AI-assisted — verify against primary sources before acting.

NVD 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.

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

Weaknesses

CWE-307

Public exploit & PoC references

All references

Source data: NVD (nvd.nist.gov), public domain. Exploit-DB.ai adds local AI analysis for defensive use only.

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