Prototype Pollution
Prototype Pollution
CWE-1321
Overtime trend (NVD)
CVSS severity (NVD, All Time)
Per technology (GHSA, All time)
- 91%-NPM
- 2%-Composer
- 2%-Maven
- 3%-Others
Short description
Extended description
By adding or modifying attributes of an object prototype, it is possible to create attributes that exist on every object, or replace critical attributes with malicious ones. This can be problematic if the product depends on existence or non-existence of certain attributes, or uses pre-defined attributes of object prototype (such as hasOwnProperty, toString or valueOf).
This weakness is usually exploited by using a special attribute of objects called proto, constructor or prototype. Such attributes give access to the object prototype. This weakness is often found in code that assigns object attributes based on user input, or merges or clones objects recursively.
Best practices to prevent this CWE
Phase: Implementation
By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
Effectiveness: High
Phase: Architecture and Design
By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
Effectiveness: High
Phase: Implementation
Strategy: Input Validation
When handling untrusted objects, validating using a schema can be used.
Effectiveness: Limited
Phase: Implementation
By using an object without prototypes (via Object.create(null) ), adding object prototype attributes by accessing the prototype via the special attributes becomes impossible, mitigating this weakness.
Effectiveness: High
Phase: Implementation
Map can be used instead of objects in most cases. If Map methods are used instead of object attributes, it is not possible to access the object prototype or modify it.
