Overview
CVE-2024-51999 describes a prototype pollution vulnerability in Express.js, a minimalist web framework for Node.js. This vulnerability affects applications using the extended query parser (‘query parser’: ‘extended’) and allows attackers to inject and overwrite properties of the Object.prototype. The issue has been fixed in Express.js versions 5.2.0 and 4.22.0.
Technical Details
The vulnerability arises when the extended query parser is enabled in Express.js. With this setting, the request.query object inherits all properties from the Object.prototype. An attacker can then overwrite these inherited properties by crafting a malicious query string that includes keys matching the prototype property names. This leads to prototype pollution, potentially impacting the application’s behavior, and in some cases, leading to more severe vulnerabilities like remote code execution (RCE) depending on how the application uses those prototype properties.
Example:
An attacker could send a request like this:
/api/endpoint?__proto__.polluted=trueIf the application is vulnerable, this will set Object.prototype.polluted to true, which might influence other parts of the application.
CVSS Analysis
Due to the nature of Prototype Pollution, the CVSS score for CVE-2024-51999 is highly dependent on the specific context of the application. As of the initial publication date, a CVSS score has not been assigned. The severity is listed as N/A. However, the potential for exploitation ranges from denial of service to remote code execution, depending on the application logic and how polluted prototype properties are utilized. Therefore, upgrading is highly recommended, regardless of the listed score.
Possible Impact
The impact of CVE-2024-51999 can vary depending on how the application utilizes the Object.prototype and the values that are injected. Potential impacts include:
- Denial of Service (DoS): By polluting critical prototype properties, an attacker can cause the application to crash or become unresponsive.
- Information Disclosure: Modifying prototype properties might reveal sensitive information.
- Remote Code Execution (RCE): In some cases, prototype pollution can be chained with other vulnerabilities to achieve remote code execution. This is particularly concerning if the application uses properties derived from the prototype in a way that allows for code injection.
- Authentication Bypass: Polluted properties could be leveraged to bypass authentication or authorization checks.
Mitigation or Patch Steps
The primary mitigation for CVE-2024-51999 is to upgrade your Express.js application to version 5.2.0 or 4.22.0 or later. These versions contain a fix for the prototype pollution vulnerability. If upgrading is not immediately possible, consider implementing the following workarounds:
- Disable the extended query parser: If possible, disable the extended query parser by setting
'query parser'to'simple'or another safe alternative. This will prevent the vulnerability from being exploited. - Input Validation: Sanitize and validate all user-supplied input, especially query parameters. Specifically, check for and reject any query parameters that attempt to modify properties of the
Object.prototype(e.g., parameters containing__proto__,constructor, orprototype). - Object Freezing: Freeze the Object prototype if possible, preventing modifications. However, this could have widespread compatibility issues and is generally not recommended.
