CVE-2021-23807: Prototype Pollution in node-jsonpointer

The vulnerability stems from two key issues: 1) In setter, the prototype pollution guard only checked fixed positions in the pointer array (indexes 1 and 2), failing to handle multi-segment paths and array-based components. 2) In compilePointer, the lack of type validation for array elements allowed attackers to use nested arrays as pointer components, causing type mismatches (array vs string) that bypassed security checks. The patch added iterative checks for dangerous properties in all pointer positions and strict type validation for pointer components, confirming these functions were the attack surface.