CVE-2021-20085: 
JavaScript vulnerability analysis and mitigation

Backbone-query-parameters version 0.4.0 contains a prototype pollution vulnerability (CVE-2021-20085) that allows malicious users to inject properties into Object.prototype. The vulnerability was discovered and disclosed in December 2020 by Tenable Network Security, Inc. The affected component is the backbone-query-parameters JavaScript library (GitHub).

The vulnerability exists in the _setParamValue function of backbone.queryparams.js where improper handling of query string parameters allows for prototype pollution. The vulnerability has a CVSS v3.1 Base Score of 8.8 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The issue is classified as CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes) (NVD).

Successful exploitation of this vulnerability allows attackers to inject properties into Object.prototype, which can lead to application-wide JavaScript object pollution. This could potentially result in security bypass, denial of service, or execution of arbitrary code depending on the application context (GitHub).

The vulnerability can be exploited by sending specially crafted query parameters to applications using the vulnerable backbone-query-parameters library. Example exploit paths include using ?proto.test=test or ?constructor.prototype.test=test in URLs (GitHub).

Users should upgrade to a patched version of backbone-query-parameters if available, or implement input validation to prevent prototype pollution attacks. If upgrading is not possible, carefully validate and sanitize all query parameters before processing (NVD).