CVE-2020-7707: 
JavaScript vulnerability analysis and mitigation

The package property-expr before version 2.0.3 contains a Prototype Pollution vulnerability (CVE-2020-7707). This vulnerability was discovered on January 21, 2020, and affects the setter function within the package. The vulnerability allows attackers to manipulate JavaScript language construct prototypes through property injection (MITRE, Snyk).

The vulnerability exists in the setter function of the property-expr package. When handling object properties, the function fails to properly validate paths containing special properties like 'proto', 'constructor', or 'prototype'. This allows an attacker to perform prototype pollution attacks. The vulnerability has been assigned a CVSS v3.1 base score of 9.8 (Critical), indicating its severe impact. The attack vector is network-based with low attack complexity and requires no privileges or user interaction (Snyk).

Successful exploitation of this vulnerability can lead to multiple severe consequences: Denial of Service (DoS) by manipulating Object.prototype properties that are implicitly called for various operations, Remote Code Execution (RCE) in cases where the codebase evaluates and executes specific object attributes, and Property Injection where an attacker can pollute security-critical properties such as privileges or tokens (Snyk).

The vulnerability has been patched in version 2.0.3 and later. The fix includes adding validation checks for dangerous property paths like 'proto', 'constructor', and 'prototype'. Organizations should upgrade to version 2.0.6 or higher. Additional recommended preventive measures include freezing the prototype using Object.freeze(Object.prototype), requiring schema validation of JSON input, avoiding unsafe recursive merge functions, and considering the use of objects without prototypes or using Map instead of Object (Snyk).