CVE-2020-7679 in casperjs
Summary
by MITRE
The mergeObjects utility function is susceptible to Prototype Pollution.
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Analysis
by VulDB Data Team • 10/26/2020
The CVE-2020-7679 vulnerability represents a critical prototype pollution flaw within the mergeObjects utility function, which fundamentally compromises the integrity of JavaScript applications that rely on object merging operations. This vulnerability allows attackers to manipulate the prototype chain of objects, enabling them to inject malicious properties into the Object.prototype object itself. When the mergeObjects function processes user-supplied input without proper validation, it can inadvertently pollute the prototype with attacker-controlled data, creating a persistent backdoor that affects all objects derived from the Object constructor.
The technical exploitation of this vulnerability occurs when applications use the mergeObjects utility to combine configuration objects or user input data. The flaw typically manifests when the function iterates through object properties and assigns them directly to the target object without checking if those properties correspond to prototype pollution vectors. Attackers can craft malicious input that includes properties like _proto_ or constructor, which when processed by the vulnerable merge function, can modify the prototype chain. This creates a dangerous scenario where any object in the application can be manipulated through prototype pollution, as all objects inherit from Object.prototype. The vulnerability aligns with CWE-471, which specifically addresses the issue of objects being modified in ways that affect the prototype chain, and can be mapped to ATT&CK technique T1546.1001 for prototype pollution attacks.
The operational impact of CVE-2020-7679 extends far beyond simple data corruption, as prototype pollution can lead to severe consequences including arbitrary code execution, denial of service, and privilege escalation attacks. Applications that utilize the affected mergeObjects function may experience unexpected behavior when processing legitimate user input, as the polluted prototype can cause unpredictable interactions with other parts of the codebase. The vulnerability can be particularly dangerous in server-side applications where user input is processed through the merge function, as it allows attackers to manipulate core JavaScript object behavior and potentially gain unauthorized access to sensitive data or system resources. Additionally, the effects of prototype pollution can persist across multiple requests and sessions, making it a particularly insidious threat that can undermine the security posture of entire applications.
Mitigation strategies for CVE-2020-7679 should focus on both immediate code-level fixes and broader architectural improvements. Developers must implement proper input validation and sanitization within the mergeObjects utility function, ensuring that property names like _proto_ and constructor are explicitly rejected or filtered out during object merging operations. The recommended approach involves adding checks to prevent prototype pollution by either using Object.freeze() on the prototype chain, implementing a whitelist of allowed properties, or employing safer object merging techniques that avoid direct prototype manipulation. Organizations should also consider upgrading to patched versions of the affected libraries, as many popular JavaScript utility libraries have released updates that address this specific vulnerability. Security teams should monitor application logs for unusual object behavior patterns and implement runtime protections that can detect and prevent prototype pollution attempts. The solution aligns with security best practices outlined in OWASP Top 10 and should be integrated into the application security testing process to prevent similar vulnerabilities from emerging in future code releases.