CVE-2018-3751 in merge-recursive
Summary
by MITRE
The utilities function in all versions <= 0.3.0 of the merge-recursive node module can be tricked into modifying the prototype of Object when the attacker can control part of the structure passed to this function. This can let an attacker add or modify existing properties that will exist on all objects.
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Analysis
by VulDB Data Team • 02/24/2020
The vulnerability identified as CVE-2018-3751 resides within the merge-recursive node module, specifically affecting versions 0.3.0 and earlier. This issue represents a critical prototype pollution vulnerability that stems from improper handling of object merging operations within the utility functions of this npm package. The flaw allows attackers to manipulate the prototype chain of JavaScript objects through crafted input data, creating a persistent security risk that can affect all subsequent object instantiations within the application's runtime environment.
The technical mechanism behind this vulnerability involves the manipulation of object property names during the merge process, particularly when the merge-recursive function processes user-controllable data structures. When an attacker can influence the structure passed to the utility function, they can inject properties with names that match prototype properties such as constructor, toString, or other built-in object methods. This occurs because the function does not properly validate or sanitize the keys being merged, allowing malicious input to directly modify the Object.prototype object. The vulnerability is classified under CWE-471 as "Modification of Assumed-Immutable Data" and represents a direct prototype pollution attack vector.
The operational impact of CVE-2018-3751 extends far beyond simple data manipulation, as prototype pollution can lead to severe consequences including remote code execution, denial of service, and privilege escalation within affected applications. When an attacker successfully pollutes the prototype, any object created afterward may inherit the malicious properties, potentially allowing them to override core JavaScript object methods or inject malicious code execution paths. This vulnerability is particularly dangerous in server-side JavaScript environments where the merge-recursive module might process user input from API endpoints, form submissions, or configuration files. The attack can be executed through various vectors including JSON parsing of untrusted data, HTTP request parameters, or any input that flows into the vulnerable merge function, making it a widespread concern across applications using this module.
Mitigation strategies for CVE-2018-3751 require immediate action to upgrade to version 0.3.1 or later of the merge-recursive module, which contains the necessary patches to prevent prototype pollution. Organizations should implement comprehensive input validation and sanitization practices, particularly for data structures that will be processed by merge operations. The recommended approach includes implementing defensive programming techniques such as using Object.freeze() on prototype objects, validating property names before merging, and employing secure coding practices that avoid direct prototype manipulation. From an ATT&CK framework perspective, this vulnerability maps to T1059.007 for JavaScript execution and T1211 for privilege escalation through prototype pollution, making it a critical concern for security teams implementing the MITRE ATT&CK matrix for threat modeling. Additionally, organizations should conduct thorough code reviews to identify other potential prototype pollution vulnerabilities in their dependency tree and consider implementing runtime protections such as prototype pollution detection mechanisms to prevent exploitation of similar issues.