CVE-2018-16469 in Merge Package
Summary
by MITRE
The merge.recursive function in the merge package v <1.2 can be tricked into adding or modifying properties of the Object prototype. These properties will be present on all objects allowing for a denial of service attack.
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Analysis
by VulDB Data Team • 04/07/2020
The vulnerability identified as CVE-2018-16469 resides within the merge package version 1.1 and earlier, specifically targeting the merge.recursive function implementation. This flaw represents a classic prototype pollution vulnerability that exploits the way JavaScript handles object prototypes and property inheritance mechanisms. The issue occurs when the merge function processes objects that contain properties named _proto_ or constructor, allowing attackers to manipulate the prototype chain of all objects within the application context. This vulnerability falls under CWE-471 which categorizes improper modification of a prototype object, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The merge package is commonly used in Node.js applications for combining configuration objects, merging user data, and handling complex data structures, making it a critical component in many software ecosystems.
The technical exploitation of this vulnerability occurs when an attacker supplies malicious input containing prototype-polluting properties to the merge.recursive function. When the function processes these inputs, it inadvertently modifies the Object.prototype object, which serves as the foundation for all JavaScript objects. This modification allows attackers to inject arbitrary properties into all objects within the application's memory space, effectively enabling them to alter the behavior of core JavaScript objects. The impact extends beyond simple property injection, as the prototype pollution can lead to various security consequences including denial of service attacks, where applications may crash or become unresponsive due to infinite loops in prototype traversal, or more sophisticated attacks that exploit the polluted prototype chain to execute unintended code.
The operational impact of CVE-2018-16469 is significant across multiple application domains where the merge package is utilized. Applications that rely on this package for configuration merging, data object consolidation, or user input processing become vulnerable to prototype pollution attacks that can compromise system stability and potentially enable further exploitation. The vulnerability is particularly dangerous in server-side applications where user input is processed through merge operations, as it allows attackers to manipulate the prototype chain of objects that may be used in security-sensitive contexts. The denial of service aspect of this vulnerability means that even a simple attack can cause application crashes or resource exhaustion, while the prototype pollution itself can enable more complex attacks such as property injection, which can be leveraged to bypass security controls or manipulate application behavior. The widespread use of the merge package in Node.js ecosystems means that this vulnerability affected numerous applications and frameworks that depend on proper object merging functionality.
Mitigation strategies for CVE-2018-16469 primarily involve upgrading to version 1.2 or later of the merge package where the vulnerability has been addressed through proper input validation and prototype sanitization. Organizations should implement comprehensive dependency management practices to ensure all third-party packages are kept current with security patches. The remediation process should include thorough code review to identify all instances where the merge.recursive function is used with untrusted input, followed by implementing proper input validation and sanitization measures. Additionally, developers should consider using alternative libraries or implementing custom merging functions that do not suffer from prototype pollution vulnerabilities. Security monitoring should be enhanced to detect unusual object property modifications, and application-level protections such as prototype chain validation can be implemented to prevent unauthorized prototype modifications. The fix implemented in version 1.2 typically involves rejecting or sanitizing properties named _proto_ and constructor during the merge process, preventing them from being added to the prototype chain and thereby eliminating the vulnerability.