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VulnerabilityPublished Updated

CVE-2026-58271: Sync-in server · Improper Restriction of Excessive Authentication Attempts

Affects Sync-in serverSource CVE Database V5

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Not known to be exploited · CVSS 6.8 Medium : upgrade to 2.4.0 when convenient.

Data as of 5 Nov 2026, 00:01 UTC

CVSS 3.1 base score
6.8Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 12% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.4.0
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 21 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

What to do

Upgrade server and sync-in/server to 2.4.0.

Affected software

ProductAffectedFixed in
Sync-inserverAffected
  • <2.4.0
Fixed in
  • 2.4.0
GitHubsync-in/serverpkg:github/sync-in/serverOther threatsAffected
  • <2.4.0
Fixed in
  • 2.4.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade Sync-in Server to version 2.4.0 or later, where this vulnerability is patched. No other mitigation is indicated by the vendor advisory. Since this is not a cloud service, remediation depends on applying the official fix.

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.

References

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