CVE-2018-16489 in just-extend
Summary
by MITRE
A prototype pollution vulnerability was found in just-extend <4.0.0 that allows attack to inject properties onto Object.prototype through its functions.
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Analysis
by VulDB Data Team • 05/07/2020
This vulnerability represents a critical prototype pollution flaw in the just-extend npm package version 4.0.0 and earlier, which enables attackers to manipulate the Object.prototype object through unsafe object extension functions. The vulnerability stems from improper handling of nested object properties during the extension process, allowing malicious input to be injected directly into the prototype chain. When the vulnerable package processes user-controlled data through its extend functions, it fails to properly sanitize or validate the keys being used, creating a pathway for attackers to pollute the prototype with malicious properties. This type of vulnerability falls under CWE-471 which specifically addresses the issue of incorrect handling of prototype properties during object manipulation operations. The attack vector typically involves sending specially crafted data structures that contain keys designed to modify prototype behavior, particularly when the package processes objects with nested properties or arrays.
The operational impact of this vulnerability extends far beyond the immediate package scope, as prototype pollution can lead to severe downstream consequences in applications that rely on standard JavaScript object behavior. When Object.prototype is polluted, all objects in the application inherit the malicious properties, potentially causing unexpected behavior in application logic, breaking existing functionality, or enabling more sophisticated attacks such as denial of service through prototype manipulation. Attackers can exploit this weakness to modify core JavaScript object methods, inject malicious code execution points, or manipulate application flow control. The vulnerability aligns with ATT&CK technique T1059.007 which describes the use of scripting languages for execution, as polluted prototypes can be leveraged to execute malicious code through prototype-based attack vectors. Applications using vulnerable versions of just-extend become susceptible to chain reactions where the pollution affects multiple components that depend on standard object behavior.
Mitigation strategies for this vulnerability require immediate version updates to just-extend 4.0.0 or later, which contain proper protections against prototype pollution attacks. Organizations should implement comprehensive dependency auditing to identify all instances of vulnerable package versions across their codebase and perform thorough security reviews of object extension patterns. Additional protective measures include implementing prototype validation checks in application code, sanitizing user inputs before processing through object extension functions, and using defensive programming techniques such as Object.freeze() on critical objects. Security teams should also consider implementing runtime monitoring to detect unusual prototype modifications and establish automated scanning processes to identify vulnerable dependencies in continuous integration pipelines. The vulnerability demonstrates the importance of proper input validation and the dangers of assuming that third-party libraries handle object manipulation safely, reinforcing the need for comprehensive security practices throughout the software development lifecycle.