CVE-2019-20149 in kind-of
Summary
by MITRE
ctorName in index.js in kind-of v6.0.2 allows external user input to overwrite certain internal attributes via a conflicting name, as demonstrated by 'constructor': {'name':'Symbol'}. Hence, a crafted payload can overwrite this builtin attribute to manipulate the type detection result.
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Analysis
by VulDB Data Team • 03/18/2024
The vulnerability identified as CVE-2019-20149 resides within the kind-of library version 6.0.2, specifically in the index.js file where the ctorName function processes external user input without adequate sanitization. This flaw represents a classic prototype pollution vulnerability that allows attackers to manipulate internal object attributes through carefully crafted input payloads. The issue occurs when the library accepts user-provided data and uses it to set properties on objects, particularly targeting the constructor property which serves as a fundamental attribute in javascript object type detection mechanisms. The vulnerability is particularly concerning because it directly impacts how the library determines object types, potentially allowing attackers to bypass type checking mechanisms that applications rely upon for security decisions.
The technical exploitation of this vulnerability leverages the fact that javascript objects inherit properties from their constructor's prototype chain, and when an attacker can control the constructor property of an object, they gain the ability to manipulate how type detection functions behave. In the specific case demonstrated by the payload 'constructor': {'name':'Symbol'}, the attacker is able to overwrite the built-in constructor attribute with a custom value that changes the behavior of type detection logic. This type of prototype pollution can lead to various security implications including bypassing input validation, manipulating object behavior, and potentially enabling further exploitation vectors. The vulnerability maps directly to CWE-471 which describes the weakness of "Modification of Externally-Controlled Properties" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript" when exploited in web contexts.
The operational impact of this vulnerability extends beyond simple type detection manipulation, as it can enable attackers to craft sophisticated attacks that exploit the broader implications of prototype pollution within javascript environments. Applications using vulnerable versions of kind-of may experience unexpected behavior when processing user input, potentially leading to security bypasses in validation routines, unexpected code execution paths, or manipulation of object-oriented programming patterns that depend on reliable type detection. The vulnerability is particularly dangerous in server-side javascript environments where user input flows through the library and may be processed in security-sensitive contexts. Organizations should consider the broader implications of prototype pollution attacks when assessing their security posture, as this vulnerability can serve as a foundation for more complex exploitation techniques.
Mitigation strategies for CVE-2019-20149 should focus on immediate remediation through library updates to versions that address the prototype pollution issue, typically version 6.0.3 or later. Security teams should implement comprehensive input validation and sanitization measures to prevent external user data from reaching vulnerable code paths, particularly in applications that process untrusted input through javascript type detection libraries. The implementation of prototype pollution detection mechanisms and regular security scanning of npm dependencies can help identify similar vulnerabilities in other libraries. Additionally, developers should avoid direct assignment of user-controlled data to object properties that may influence type detection or object behavior, and consider implementing defensive programming patterns that protect against prototype pollution attacks through object freezing or property descriptor restrictions. Organizations should also monitor for similar vulnerabilities in other javascript utility libraries that may exhibit comparable prototype pollution characteristics.