CVE-2020-28499 in merge Package
Summary
by MITRE • 02/18/2021
All versions of package merge are vulnerable to Prototype Pollution via _recursiveMerge .
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Analysis
by VulDB Data Team • 03/03/2021
The vulnerability identified as CVE-2020-28499 affects the merge package, a widely used JavaScript library for combining objects and arrays. This issue stems from a prototype pollution flaw that allows attackers to manipulate the prototype of objects during the merge process. The vulnerability specifically manifests through the _recursiveMerge function which fails to properly validate or sanitize input data before incorporating it into existing object prototypes. This type of vulnerability falls under the Common Weakness Enumeration category CWE-471, which describes situations where a program modifies a data structure in a way that affects the behavior of the program itself. The merge package is commonly used across numerous applications and frameworks, making this vulnerability particularly dangerous as it can affect a vast ecosystem of software dependencies.
The technical implementation of this prototype pollution vulnerability occurs when the _recursiveMerge function processes user-controlled input without proper validation. Attackers can inject malicious properties into the Object.prototype through carefully crafted input data that gets merged into existing objects. When subsequent code attempts to iterate over object properties, these polluted prototype properties are inadvertently included in the iteration, potentially causing unexpected behavior or execution of malicious code. The vulnerability is particularly concerning because it can be exploited in various contexts including web applications, server-side code, and even in client-side JavaScript environments where the merge function is utilized for data processing. This type of attack vector aligns with the MITRE ATT&CK framework's technique T1068, which covers 'Exploitation for Privilege Escalation' and T1590, which covers 'Network Reconnaissance' as attackers often use such vulnerabilities to gain deeper access to systems.
The operational impact of CVE-2020-28499 extends beyond simple data corruption, as prototype pollution can lead to more severe consequences including denial of service conditions, information disclosure, and potentially remote code execution depending on the application context. Applications that rely on the merge package for processing user input are at risk, especially those that do not properly validate or sanitize data before merging operations. The vulnerability is particularly dangerous in environments where the merge function is used to process configuration data, user preferences, or API responses that may contain untrusted input. Security teams should consider this vulnerability as a critical risk factor in their application security assessments, particularly in systems where JavaScript-based applications process external data through merge operations. The widespread adoption of the merge package across the Node.js ecosystem means that organizations using this library are likely to be impacted, requiring immediate attention and remediation efforts to prevent potential exploitation.
Organizations should implement immediate mitigations including updating to patched versions of the merge package, implementing input validation and sanitization measures, and conducting comprehensive security assessments of applications that utilize this library. The fix typically involves adding proper validation checks to prevent pollution of object prototypes during merge operations, often through the use of hasOwnProperty checks or by using safer object manipulation methods. Additionally, security monitoring should be enhanced to detect anomalous patterns in object property access that may indicate prototype pollution attempts. The vulnerability highlights the importance of dependency management and regular security audits, as prototype pollution vulnerabilities often go undetected until they are actively exploited in the wild. Given the nature of this vulnerability, organizations should also consider implementing runtime protections and application whitelisting to prevent exploitation of similar issues in other libraries that may be susceptible to prototype pollution attacks.