CVE-2021-20089 in purl
Summary
by MITRE • 04/24/2021
Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in purl 2.3.2 allows a malicious user to inject properties into Object.prototype.
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Analysis
by VulDB Data Team • 04/29/2021
Prototype pollution vulnerabilities occur when an application fails to properly validate or sanitize user input that is used to modify object prototype properties. In the case of CVE-2021-20089 affecting purl version 2.3.2, this vulnerability manifests when the library processes user-supplied data without adequate safeguards, allowing attackers to inject malicious properties directly into the Object.prototype chain. The flaw stems from inadequate input validation mechanisms within the purl library's handling of URL parsing and parameter processing. When user-controlled data is passed through the library's parsing functions, it can inadvertently modify the prototype object itself rather than the intended target object. This creates a dangerous scenario where any subsequent object creation or property access can be manipulated by the attacker. The vulnerability is particularly concerning because it affects the fundamental object model of javascript applications, potentially enabling attackers to override critical methods or properties that are used throughout the application's execution. This type of vulnerability is classified under CWE-471 which specifically addresses the improper control of modifications to object prototype attributes. The impact extends beyond simple data corruption as it can enable more sophisticated attacks such as method hijacking, where attackers can redirect function calls to malicious code. From an operational perspective, this vulnerability can be exploited across various attack vectors including web applications, server-side processing, and client-side javascript environments where purl is utilized for URL manipulation. The attack typically involves crafting specially formatted input that, when processed by the vulnerable library, pollutes the prototype with malicious properties. This can lead to denial of service conditions, unauthorized access, or even remote code execution depending on the application's architecture and how it utilizes the polluted prototype properties. The vulnerability aligns with several ATT&CK techniques including T1059.007 for scripting and T1566 for social engineering through malicious links. Organizations using purl 2.3.2 or earlier versions should immediately upgrade to patched releases that implement proper input validation and sanitization. Mitigation strategies include implementing strict input validation, using secure coding practices that prevent prototype modifications, and employing runtime protections such as prototype lockdown mechanisms. Additionally, security monitoring should be enhanced to detect unusual prototype modifications and input processing patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of validating all user-supplied input at multiple layers of application architecture, particularly when dealing with libraries that handle data parsing and manipulation.