CVE-2026-58272 Overview
CVE-2026-58272 is an observable timing discrepancy vulnerability [CWE-208] affecting Sync-in Server, an open-source platform for file storage, sharing, collaboration, and syncing. Versions prior to 2.4.1 return authentication failures for nonexistent accounts without performing the bcrypt password comparison used for existing accounts. This difference in response time allows unauthenticated attackers to enumerate valid usernames and email addresses. The maintainers released version 2.4.1 to remediate the issue.
Critical Impact
Unauthenticated remote attackers can enumerate valid user accounts by measuring login response times, enabling targeted credential-stuffing, password-spraying, and phishing campaigns against confirmed users.
Affected Products
- Sync-in Server versions prior to 2.4.1
Discovery Timeline
- 2026-09-21 - CVE-2026-58272 published to NVD
- 2026-09-23 - Last updated in NVD database
Technical Details for CVE-2026-58272
Vulnerability Analysis
The vulnerability resides in the Sync-in Server login endpoint. When a client submits credentials, the server processes existing and nonexistent accounts along different code paths. Requests for existing accounts trigger a bcrypt hash comparison against the stored password. Requests for nonexistent accounts short-circuit and return an authentication failure without invoking bcrypt.
Bcrypt is intentionally slow, adding measurable latency to any authentication attempt that reaches the comparison step. Because that latency is absent for unknown accounts, response times for valid and invalid usernames diverge in a consistent, measurable way. An attacker can automate login requests against a candidate list and classify each response by timing alone.
The issue is classified under CWE-208: Observable Timing Discrepancy. While the flaw does not directly disclose passwords, it lowers the cost of downstream attacks by turning username guessing into a deterministic oracle.
Root Cause
The root cause is asymmetric authentication logic. The login handler validates account existence before performing password verification, and only executes the expensive bcrypt comparison when a matching account is found. This produces two distinct response-time distributions that map directly to account validity.
Attack Vector
Exploitation requires network access to the Sync-in Server login endpoint and no authentication or user interaction. An attacker submits authentication requests with candidate usernames or email addresses and records server response latency. Requests that trigger bcrypt take measurably longer than those that do not, revealing which identifiers correspond to real accounts. The enumerated list then feeds credential-stuffing, password-spraying, or phishing operations.
No verified public exploit code has been published. Refer to the GitHub Security Advisory GHSA-29hq-23m2-2j47 for maintainer-provided technical details.
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Stop Identity AttacksDetection Methods for CVE-2026-58272
Indicators of Compromise
- High volumes of failed login attempts from a single source or narrow set of IP addresses against the Sync-in Server authentication endpoint.
- Sequential or dictionary-ordered login attempts using varied usernames or email addresses with identical or missing password fields.
- Requests to the login endpoint that show repeated patterns consistent with automated timing measurement rather than interactive user behavior.
Detection Strategies
- Alert on authentication endpoints receiving requests at rates exceeding normal user login behavior from a single client.
- Monitor for skewed ratios of failed-to-successful logins and unusually broad username coverage from one source.
- Correlate enumeration bursts with subsequent credential-stuffing or password-spraying attempts using the same or overlapping IP infrastructure.
Monitoring Recommendations
- Capture application-layer logs from the Sync-in Server login endpoint including timestamp, source IP, submitted username, and response outcome.
- Forward authentication logs to a centralized analytics platform to baseline normal login patterns and detect enumeration bursts.
- Track post-enumeration behavior such as successful logins from novel IPs to identifiers that were previously probed.
How to Mitigate CVE-2026-58272
Immediate Actions Required
- Upgrade Sync-in Server to version 2.4.1 or later, which contains the patch.
- Review authentication logs for prior enumeration activity and force password resets for any accounts confirmed to have been probed and subsequently accessed.
- Enforce multi-factor authentication for all Sync-in Server accounts to reduce the value of enumerated identifiers.
Patch Information
The Sync-in maintainers released Sync-in Server version 2.4.1 with a fix that removes the observable timing discrepancy in the login endpoint. Details are documented in the GitHub Security Advisory GHSA-29hq-23m2-2j47. Administrators should upgrade to 2.4.1 or later at the earliest opportunity.
Workarounds
- Apply rate limiting and progressive backoff to the login endpoint to increase the cost of automated timing probes.
- Place the Sync-in Server login endpoint behind a web application firewall or reverse proxy configured to block high-frequency authentication requests from single sources.
- Restrict access to the login endpoint to trusted network ranges or via VPN where operationally feasible until the patch is applied.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
