CVE-2026-58271Public exploitNetwork attack vectorHinoki check available

Account takeover via frozen TOTP failure counter

Published Sep 21, 2026 · Updated Sep 21, 2026

Improper authentication throttling in Sync-in Server before 2.4.0 allows remote authenticated users to obtain full sessions by guessing TOTP codes. SyncClientsManager.register() passes failed TOTP checks to updateAccesses(), whose freeze branch writes passwordAttempts back unchanged so the ten-attempt lockout never fires. Valid credentials, a TOTP-enabled account, desktop sync permission, and endpoint reachability are required; a correct guess yields a client token exchangeable for a JWT and permits MFA removal.

CVSS severity6.8
Medium
EPSS probability0.22%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Improper authentication throttling in Sync-in Server before 2.4.0 allows remote authenticated users to obtain full sessions by guessing TOTP codes. SyncClientsManager.register() passes failed TOTP checks to updateAccesses(), whose freeze branch writes passwordAttempts back unchanged so the ten-attempt lockout never fires. Valid credentials, a TOTP-enabled account, desktop sync permission, and endpoint reachability are required; a correct guess yields a client token exchangeable for a JWT and permits MFA removal.

The record

CVE
CVE-2026-58271
Published
Sep 21, 2026
Updated
Sep 21, 2026
Vendor
Sync-in
Product
Sync-in Server
Classifications
CWE-307, T1110.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 21, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Sync-in · Sync-in Serverversion=< 2.4.0

Published CVSS scores

6.8GitHubCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-307Improper Restriction of Excessive Authentication Attempts
T1110.001Password Guessing

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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