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The vulnerability (CVE-2025-xxxx) in the elysia-cors library up to version 1.3.0 stems from an improper origin validation mechanism. The library’s function for validating incoming request origins against a whitelist uses a flawed substring matching algorithm instead of a strict equality or regex-based boundary check. Specifically, when comparing the `Origin` header value to a configured allowed origin like “example.com”, the check `allowedOrigin.includes(incomingOrigin)` is used. This logic incorrectly returns true for malicious origins such as “notexample.com” or “example.common.net” because the string “example.com” is contained within them. Consequently, the Access-Control-Allow-Origin header is set to the malicious origin, bypassing the Same-Origin Policy and enabling attackers to perform unauthorized cross-origin requests to retrieve sensitive user data from a vulnerable application.
Platform: Elysia.js
Version: <=1.3.0
Vulnerability: CORS Bypass
Severity: Moderate
date: 2025-08-20
Prediction: 2025-09-03
What Undercode Say:
`curl -H “Origin: http://notexample.com” -v http://vulnerable-site.com/api/data`
`const app = new Elysia().use(cors({ origin: [‘example.com’] })) // Vulnerable config`
`// Patch: Use strict comparison or regex with anchors: ^example.com$`
How Exploit:
Craft HTTP request with malicious Origin header pointing to a domain that contains the whitelisted string as a substring.
Protection from this CVE:
Upgrade elysia-cors. Implement strict origin validation on server-side.
Impact:
Unauthorized cross-origin data access, potential information disclosure.
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Sources:
Reported By: github.com
Extra Source Hub:
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