Username Enumeration Vulnerability in @sync-in/server: Timing Attack Exploit
Summary
GHSA-43fj-qp3h-hrh5: Sync-in Server has Username Enumeration via Timing Attack. Affects @sync-in/server versions < 2.2.0. Fixed in 2.2.0. How to fix ↓
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Background
The @sync-in/server package is a backend service designed for user authentication and management within applications. It provides APIs for user login, registration, and profile management. However, it is susceptible to a timing attack that allows attackers to enumerate valid usernames by analyzing response times from the authentication endpoint.
Vulnerability Detail
The vulnerability arises from a logic flaw in the /api/auth/login endpoint, where the application returns responses at different times based on whether the username exists. Valid usernames trigger a response time of approximately 350-400ms, while invalid usernames return responses in about 95-100ms. This discrepancy allows attackers to infer valid usernames through timing analysis, significantly weakening the application's security and facilitating targeted brute-force attacks.
How To Fix
Latest published version: 2.6.0 as of 23 Oct 2026
npm install @sync-in/server@2.6.0Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
2.2.0
This is the first release that contains the fix.
npm install @sync-in/server@2.2.0Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, implement rate limiting on the /api/auth/login endpoint to reduce the effectiveness of timing attacks. Additionally, consider adding a uniform delay for all responses from the endpoint, regardless of whether the username is valid or not.
Conclusion
The @sync-in/server package has a significant vulnerability that allows for username enumeration through timing attacks. It is crucial to update to the patched version 2.2.0 or later to mitigate this risk. Implementing workarounds such as rate limiting and uniform response delays can also help enhance security until the update is applied.
See every vulnerability recorded for @sync-in/server →
FAQ
A timing attack is a type of side-channel attack where an attacker gains information about a system by measuring the time it takes to execute cryptographic algorithms or responses to requests.
An attacker can exploit this vulnerability by sending multiple login requests with different usernames and measuring the response times to determine which usernames are valid.
The consequences include unauthorized access attempts, targeted brute-force attacks, and increased risk of social engineering attacks against valid users.
Yes, you can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time. You can check if your application is affected by this vulnerability using the Vulert playground without any signup.
The CVSS score of this vulnerability is 6.9, indicating a moderate severity level.
References
Related vulnerabilities
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