CVE-2025-66456

|
CVE-2025-66456 elysiajs elysia vulnerability security critical severity prototype pollution RCE CVE database javascript security typescript security

Summary

CVE-2025-66456 describes a critical prototype pollution vulnerability affecting Elysia.js versions 1.4.0 through 1.4.16. This vulnerability, present in the mergeDeep function, allows attackers to potentially achieve Remote Code Execution (RCE) when combined with other vulnerabilities by manipulating the __proto__ property during schema validation.

Technical Details

The vulnerability stems from the mergeDeep function within Elysia.js, which is used to merge the results of schema validations. A prototype pollution occurs when merging two standard schema validations with the same key, specifically when an 'any' type is used as a standalone guard. This allows for the injection and manipulation of the __proto__ property of JavaScript objects. The issue arises due to the order of merging operations, which permits overwriting properties in the prototype chain.

Specifically, if a schema validation includes an 'any' type guard, it becomes possible to inject properties into the Object prototype. When combined with GHSA-8vch-m3f4-q8jf, this prototype pollution can be leveraged to achieve Remote Code Execution (RCE). An attacker can craft malicious input that, when processed by the vulnerable mergeDeep function, injects arbitrary code into the prototype, leading to code execution on the server.

Affected Products and Versions

  • Elysia.js versions 1.4.0 through 1.4.16

Impact Assessment

Successful exploitation of CVE-2025-66456 can lead to severe consequences, including:

  • Remote Code Execution (RCE): An attacker can execute arbitrary code on the server, potentially gaining full control of the system.
  • Data Breach: Sensitive data stored on the server could be accessed and exfiltrated by the attacker.
  • Denial of Service (DoS): The attacker could crash the server or make it unavailable to legitimate users.
  • System Compromise: The attacker could compromise the entire system, including databases and other critical components.

Remediation

Immediate Actions

  • Upgrade to Version 1.4.17 or later: This version contains a fix for the prototype pollution vulnerability.
  • Review and Sanitize Input: Carefully review all user input and ensure that it is properly sanitized to prevent malicious code injection.

Long-term Solutions

  • Implement Robust Input Validation: Implement comprehensive input validation to prevent malicious input from reaching the vulnerable mergeDeep function.
  • Monitor for Suspicious Activity: Monitor your systems for any signs of suspicious activity, such as unexpected code execution or unauthorized access.

References

Detection & Scanning

Detecting this vulnerability requires careful analysis of your Elysia.js application's dependencies and configuration. Look for instances of Elysia.js versions 1.4.0 through 1.4.16. Furthermore, inspect your schema validation logic for the use of 'any' type guards in conjunction with the mergeDeep function. Regular security scanning can help identify vulnerable dependencies and potential attack vectors.

Scan Your Website

Secably AI Scanner can detect this and 50+ other vulnerabilities automatically.

Start Free Scan

Scan Your Website for Vulnerabilities

Discover security issues before attackers do. Our AI-powered scanner checks for the vulnerabilities discussed in this guide and more.

Start Free Scan