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CVE-2025-55183 exploits a flaw in Next.js App Router endpoints using Server Actions. In affected versions, when a malicious HTTP request is crafted and sent to such endpoints, the server may return the compiled source code of the Server Function instead of executing it. This occurs due to improper handling in the request processing pipeline, specifically in serialization or deserialization. The vulnerability stems from dependent React packages (versions 19.0.0 to 19.2.1) used by Next.js. Attackers can manipulate headers or parameters in requests to trigger this behavior. The server responds with JavaScript source code, exposing business logic. Hardcoded secrets like API keys may be leaked if embedded directly in the function code. The issue affects App Router endpoints without requiring authentication, making publicly accessible routes vulnerable. This could lead to intellectual property theft or further attacks. Patched versions fix the request handling to prevent source code leakage by validating inputs and securing response serialization.
Platform: Next.js
Version: 15.x 16.x
Vulnerability: Source Code Exposure
Severity: Medium
Date: Dec 11 2025
Prediction: Patched Dec 2025
What Undercode Say:
Analytics:
Bash commands:
next –version
npm list next
npm install [email protected]
Codes:
// Example Server Action in Next.js App Router
export async function myAction() {
// Business logic here
}
how Exploit:
Craft malicious HTTP requests to App Router endpoints using tools like curl with modified headers or parameters to trigger source code leakage in responses.
Protection from this CVE:
Update to patched Next.js versions, avoid hardcoding secrets in Server Actions, implement input validation, and use environment variables for sensitive data.
Impact:
Source code disclosure, business logic exposure, potential secret leakage, and intellectual property theft.
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Sources:
Reported By: github.com
Extra Source Hub:
Undercode
