CVE-2026-58271

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.

Overview

State: PUBLISHED
Assigner (CNA): GitHub_M
CVSS severity: MEDIUM
CVSS score: 6.8 / 10
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
Effective score: 6.8 / 10 MEDIUM source: CNA overview
CWE(s): CWE-307
Reserved: 2026-06-29
Published: 2026-09-21 19:50 UTC
Last updated: 2026-09-21 19:50 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/58xxx/CVE-2026-58271.json

NVD triage scoring NVD CVE 2.0

Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.

NVD published: 2026-09-21 20:17:26 UTC
NVD last modified: 2026-09-21 20:17:26 UTC
NVD CVSS v3.1: 6.8 / 10 MEDIUM source: security-advisories@github.com
NVD CVSS vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
Exploitability subscore: 1.6 / 10
Impact subscore: 5.2 / 10

European Union Vulnerability Database ENISA EUVD

ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.

EUVD ID: EUVD-2026-84112
Assigner: GitHub_M
Published: Sep 21, 2026, 7:50:14 PM
Updated: Sep 21, 2026, 7:50:14 PM
EUVD base score (CVSS 3.1): 6.8 / 10
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
EUVD-reported EPSS: 0.0000
Vendors: Sync-in
Products: Server (< 2.4.0)

ENISA 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.

EUVD references (1)

https://github.com/Sync-in/server/security/advisories/GHSA-274f-6w77-8qm9

Affected products (1)

Vendor	Product	Versions	Platforms
Sync-in	server	`< 2.4.0` (affected)	—

Vendor references (1)

References embedded in the original CVE record by the assigning CNA.

https://github.com/Sync-in/server/security/advisories/GHSA-274f-6w77-8qm9 x_refsource_CONFIRM

Web references (0)

DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.

No web references attached yet.

NVD-tagged references (1)

Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.

https://github.com/Sync-in/server/security/advisories/GHSA-274f-6w77-8qm9 security-advisories@github.com

Remediations (10)

CVE-2026-58271 | Vulnerability Database | Aqua Security

web:avd.aquasec.com

CVE-2026-58271 Vulnerability, Severity 0 N/A, Improper Restriction of Excessive Authentication Attempts

2026-09-22 17:11 UTC
Microsoft and Adobe Patch Tuesday, August 2026 Security Update Review

web:blog.qualys.com

The August 2026 Microsoft Patch Tuesday release delivers security fixes for vulnerabilities affecting a wide range of Microsoft products and services.

2026-09-22 17:11 UTC
CVE-2026-58271: Sync-in Server Vulnerability - CVETodo

web:cvetodo.com

CVE-2026-58271 is a CVSS 6.8 medium-severity vulnerability in Sync-in Server. Full technical analysis, mitigations , and exploit status — updated in real time.

2026-09-22 17:11 UTC
The Patch Is Not Enough: SharePoint's ToolShell Chain Steals Keys That ...

web:forkast.news

The ToolShell chain steals MachineKey material that survives the patch itself - meaning organizations that only applied the fix remain compromised until cryptographic keys are rotated across the entire SharePoint farm.

2026-09-22 17:11 UTC
Security Update Guide - Microsoft

web:msrc.microsoft.com

The Microsoft Security Response Center (MSRC) investigates all reports of security vulnerabilities affecting Microsoft products and services, and provides the information here as part of the ongoing effort to help you manage security risks and help keep your systems protected.

2026-09-22 17:11 UTC
Security Update Guide - Microsoft Security Response Center

web:msrc.microsoft.com

Access Microsoft Security Response Center's guide to address vulnerabilities, manage security risks, and keep your systems protected with the latest updates.

2026-09-22 17:11 UTC
Microsoft Patch Tracker (September 2026): Exploit-Ranked | Senserva

web:senserva.com

Every Microsoft security patch (KB) and the CVEs it fixes, with severity, CVSS, and CISA KEV status. Cross-linked to the CVE reference.

2026-09-22 17:11 UTC
Critical Patches Issued for Microsoft Products, August 11, 2026

web:www.cisecurity.org

<p>Multiple vulnerabilities have been discovered in Microsoft products, the most severe of which could allow for remote code execution. Successful exploitation of the most severe of these vulnerabilities could result in an attacker gaining the same privileges as the logged-on user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or ...

2026-09-22 17:11 UTC
National Vulnerability Database | NIST

web:www.nist.gov

NIST maintains the National Vulnerability Database (NVD), a repository of information on software and hardware flaws that can compromise computer security. This is a key piece of the nation's cybersecurity infrastructure.

2026-09-22 17:11 UTC
CVE-2026-58271: Sync-in server: Sync-in Server is an open ... - Rapid7

web:www.rapid7.com

CVE-2026-58271 : Sync-in server: Sync-in Server is an open-source platform for file storage, sharing, collaboration, and syncing. View severity, references, and remediation details from Rapid7.

2026-09-22 17:11 UTC

AI Forensic Analysis

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Raw JSON

The full cvelistV5 record. Download as CVE-2026-58271.json.

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "server",
          "vendor": "Sync-in",
          "versions": [
            {
              "status": "affected",
              "version": "< 2.4.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 6.8,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-307",
              "description": "CWE-307: Improper Restriction of Excessive Authentication Attempts",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-21T19:50:14.539Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/Sync-in/server/security/advisories/GHSA-274f-6w77-8qm9",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/Sync-in/server/security/advisories/GHSA-274f-6w77-8qm9"
        }
      ],
      "source": {
        "advisory": "GHSA-274f-6w77-8qm9",
        "discovery": "UNKNOWN"
      },
      "title": "@sync-in/server vulnerable to TOTP Brute-Force via `POST /api/app/sync/register`"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-58271",
    "datePublished": "2026-09-21T19:50:14.539Z",
    "dateReserved": "2026-06-29T21:54:30.332Z",
    "dateUpdated": "2026-09-21T19:50:14.539Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}