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The vulnerability exists in the `mp.addEventHandler` function of the mpregular framework. This function is designed to add event handlers to components but insecurely handles user input when setting nested properties. An attacker can supply a crafted payload containing special characters like periods (e.g., __proto__.polluted) as part of the event handler configuration. The function’s logic does not properly validate this input before using it to assign values to object properties. Consequently, instead of setting a property on the intended event handler object, the assignment operation traverses the prototype chain and modifies the base Object.prototype. This pollution affects all objects in the application, potentially introducing unexpected properties or altering the behavior of existing methods, leading to a denial of service (DoS) or, in worst-case scenarios, remote code execution.
Platform: mpregular
Version: <=0.2.0
Vulnerability: Prototype Pollution
Severity: High
date: 2025-09-24
Prediction: Patch by 2025-10-08
What Undercode Say:
npm list mpregular grep -r "mp.addEventHandler" src/
// Proof of Concept
const mp = require('mpregular');
// This pollutes Object.prototype for all objects
mp.addEventHandler('malicious', { '<strong>proto</strong>.polluted': 'yes' });
console.log(({}).polluted); // Outputs 'yes'
How Exploit:
An attacker crafts a malicious event handler registration request containing a payload like {"__proto__":{"isAdmin":true}}. If the application uses checks like `if (user.isAdmin)` on any object, the polluted property may bypass authentication. Alternatively, pollution can break application logic by overriding built-in methods, causing a crash.
Protection from this CVE:
Update mpregular to a version above 0.2.0 once a patch is released. Immediately sanitize all inputs to mp.addEventHandler, rejecting keys containing __proto__, constructor, or prototype. Use objects created with `Object.create(null)` which have no prototype, for property assignments. Employ security linters to detect unsafe patterns.
Impact:
Denial of Service (DoS) is the minimum impact, as application functionality can be disrupted. The vulnerability could potentially be leveraged for remote code execution if polluted properties influence code execution flows, such as template rendering or shell command generation. All applications using vulnerable versions are affected.
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Sources:
Reported By: github.com
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