The core vulnerability was in the generate function's property assignment logic (CWE-1321), which lacked checks for prototype-modifying properties like 'proto'. The commit diff shows the fix added a specific check for (name === 'proto' && current[name] === Object.prototype) to prevent pollution. The 'set' function is explicitly called out in PoC examples as the attack vector that triggers the vulnerable code path. Both functions work together - set() provides the external interface to modify object hierarchies, while generate() contains the unsafe implementation.