CVE-2021-25953: 
JavaScript vulnerability analysis and mitigation

Prototype pollution vulnerability in 'putil-merge' versions 1.0.0 through 3.6.6 allows attackers to cause a denial of service and may lead to remote code execution. The vulnerability was disclosed on July 14, 2021, affecting the NPM module putil-merge (WhiteSource, NVD).

The vulnerability exists in the merge() function which lacks proper validation of values passed as arguments. The function does not check for the type of object before assigning values to properties, allowing attackers to manipulate properties through the __proto__ property. This flaw enables creation of non-existent properties or manipulation of existing ones. The vulnerability has a CVSS v3.1 base score of 9.8, indicating critical severity, with attack vector being Network, low attack complexity, and no privileges or user interaction required (WhiteSource).

Successful exploitation of this vulnerability can lead to denial of service conditions and potentially remote code execution. The vulnerability affects the confidentiality, integrity, and availability of the system with high impact ratings. When exploited, the attacker can pollute the Object prototype, affecting all objects in the application (WhiteSource).

The vulnerability is exploitable by supplying malicious input that includes the __proto__ property. Due to the lack of validation before property assignment, an attacker can pollute the Object prototype by directly assigning properties to new objects. The attack vector is network-based with low complexity, requiring no privileges or user interaction (WhiteSource).

The recommended mitigation is to upgrade to version 3.7.0 of putil-merge. For those unable to upgrade immediately, implementing proper validation of object properties and checking whether assigned arguments are the Object's own properties before assignment can help mitigate the risk (WhiteSource).