Fix: issue #5756 and fixed the Typescript for baseSet function and isIndex

src/.internal/baseSet.ts

@@ -14,7 +14,7 @@ import toKey from './toKey.js'
  * @param {Function} [customizer] The function to customize path creation.
  * @returns {Object} Returns `object`.
  */
-function baseSet(object, path, value, customizer) {
+function baseSet<T>(object: T, path: string | string[], value: any, customizer?: (objValue: any, key: string, nested: T) => any): T {
   if (!isObject(object)) {
     return object
   }
@@ -24,15 +24,24 @@ function baseSet(object, path, value, customizer) {
   const lastIndex = length - 1
 
   let index = -1
-  let nested = object
+  let nested: any = object
 
   while (nested != null && ++index < length) {
     const key = toKey(path[index])
     let newValue = value
 
     if (index !== lastIndex) {
       const objValue = nested[key]
-      newValue = customizer ? customizer(objValue, key, nested) : undefined
+      // Validate key to prevent prototype pollution
+      if (!isValidKey(key)) {
+        throw new Error('Invalid key detected');
+      }
+      // Validate objValue to prevent prototype pollution
+      if (!isObject(objValue)) {
+        throw new Error('Invalid object value detected');
+      }
+
+      newValue = customizer ? customizer(objValue, key, nested) : undefined;
       if (newValue === undefined) {
         newValue = isObject(objValue)
           ? objValue
@@ -45,4 +54,10 @@ function baseSet(object, path, value, customizer) {
   return object
 }
 
-export default baseSet
+// Function to validate keys to prevent prototype pollution
+function isValidKey(key: string): boolean {
+  const disallowedKeys = ['__proto__', '__constructor__', '__prototype__'];
+  return !disallowedKeys.includes(key);
+}
+
+export default baseSet;

src/.internal/isIndex.ts

@@ -12,7 +12,7 @@ const reIsUint = /^(?:0|[1-9]\d*)$/
  * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
  * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
  */
-function isIndex(value, length) {
+function isIndex(value: any, length?: number | null): boolean {
   const type = typeof value
   length = length == null ? MAX_SAFE_INTEGER : length