CVE-2026-16266 in mongo-object
Summary
by MITRE • 07/21/2026
Versions of the package mongo-object before 3.0.3 are vulnerable to Prototype Pollution via the expandKey() function in util.js. An attacker can modify the JavaScript prototype chain by supplying a crafted property path containing special keys such as __proto__.
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Analysis
by VulDB Data Team • 07/21/2026
The vulnerability under discussion affects the mongo-object package versions prior to 3.0.3, specifically targeting a prototype pollution flaw within the expandKey() function located in util.js. This type of vulnerability represents a critical security concern that falls under the Common Weakness Enumeration category CWE-471, which classifies it as a weakness where a program modifies a data structure or object in a way that affects the behavior of other objects or functions that rely on the same prototype chain. The flaw enables attackers to manipulate JavaScript's prototype mechanism by crafting malicious property paths that contain special keys such as _proto_, effectively allowing unauthorized modification of object prototypes.
The operational impact of this vulnerability extends beyond simple data corruption, as it can lead to severe consequences in applications that process untrusted input through the mongo-object library. When an attacker supplies a specially crafted property path containing prototype pollution indicators, they can inject malicious code into the application's execution environment. This capability allows for arbitrary code execution, data manipulation, and potential privilege escalation within the affected system. The vulnerability is particularly dangerous because JavaScript prototypes are fundamental to how objects interact and inherit properties, making prototype pollution a powerful attack vector that can compromise entire application architectures.
The exploitation of this vulnerability requires minimal technical expertise but can result in significant security breaches when applications fail to properly validate input parameters. Attackers can leverage the expandKey() function to pollute prototypes with malicious payloads, potentially affecting any subsequent object creation or property access operations within the same execution context. This type of attack aligns with techniques documented in the MITRE ATT&CK framework under the T1059.007 sub-technique for 'Command and Scripting Interpreter: JavaScript', where attackers use prototype pollution to execute malicious JavaScript code. The vulnerability demonstrates how seemingly benign library functions can become attack vectors when proper input sanitization is not implemented.
Mitigation strategies should focus on upgrading to mongo-object version 3.0.3 or later, which includes patches specifically designed to prevent prototype pollution attacks. Organizations must also implement comprehensive input validation mechanisms that sanitize all user-supplied data before processing it through any library functions that may be vulnerable to prototype pollution. Additional protective measures include employing strict object property definitions using Object.freeze() and Object.preventExtensions(), implementing Content Security Policies to limit code execution, and conducting regular security audits of third-party dependencies. The vulnerability highlights the importance of maintaining up-to-date software libraries and following secure coding practices that prevent manipulation of core JavaScript objects through user input.