Home > CWE List > CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (4.18) |
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CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
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Example 1 This function sets object attributes based on a dot-separated path. (bad code)
Example Language: JavaScript
function setValueByPath (object, path, value) {
const pathArray = path.split(".");
const attributeToSet = pathArray.pop(); let objectToModify = object; for (const attr of pathArray) { if (typeof objectToModify[attr] !== 'object') { objectToModify[attr] = {}; } objectToModify = objectToModify[attr]; } objectToModify[attributeToSet] = value; return object; } This function does not check if the attribute resolves to the object prototype. These codes can be used to add "isAdmin: true" to the object prototype. (bad code)
Example Language: JavaScript
setValueByPath({}, "__proto__.isAdmin", true)
setValueByPath({}, "constructor.prototype.isAdmin", true) By using a denylist of dangerous attributes, this weakness can be eliminated. (good code)
Example Language: JavaScript
function setValueByPath (object, path, value) {
const pathArray = path.split(".");
const attributeToSet = pathArray.pop(); let objectToModify = object; for (const attr of pathArray) {
// Ignore attributes which resolve to object prototype
objectToModify[attributeToSet] = value;if (attr === "__proto__" || attr === "constructor" || attr === "prototype") {
continue;
if (typeof objectToModify[attr] !== "object") {}
objectToModify[attr] = {};
objectToModify = objectToModify[attr];} } return object; } Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.
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