Meghan Hodges
Prototype pollution is a critical vulnerability that can occur in JavaScript environments. It is an injection attack that allows attackers to modify the prototype of an object, affecting all objects derived from it. This can lead to serious security issues such as unauthorized access to data, privilege escalation, and remote code execution. Prototype pollution vulnerabilities have been found in popular JavaScript libraries, including jQuery, lodash, express, and minimist. These vulnerabilities can be exploited on both the server and client sides, making it crucial to understand and address them. By polluting the prototype, attackers can manipulate the behaviour of JavaScript programs and inject malicious properties or methods.
| Characteristics | Values |
|---|---|
| Type of vulnerability | Injection attack |
| Target | JavaScript runtimes |
| Attacker capabilities | Control default values of an object's properties, manipulate application logic, data theft, unauthorized access to data, privilege escalation, denial of service, remote code execution |
| Affected libraries | jQuery, lodash, express, minimist, hoek, node-forge |
| Defence strategies | Use new Set() or new Map() instead of object literals, use Object.create(null) to prevent inheritance from Object prototype, use Object.freeze() and Object.seal() to prevent prototype modification, remove proto property, update dependencies, strictly control parameters |
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What You'll Learn
- Prototype pollution is an injection attack that targets JavaScript runtimes
- Attackers can modify the prototype of an object, affecting all derived objects
- Attackers can control default values of an object's properties, tampering with application logic
- Prototype pollution vulnerabilities can be exploited on both the server and client sides
- Libraries vulnerable to prototype pollution include jQuery, lodash, express, minimist, and hoek
Prototype pollution is an injection attack that targets JavaScript runtimes
In JavaScript, objects inherit properties and behaviors from a prototype. Each object has a prototype, and if a property or method is not found on the object itself, JavaScript looks for it in its prototype and then moves up the prototype chain until it finds the property or reaches the top-level Object.prototype. Prototype pollution occurs when an attacker modifies the prototype of a commonly used object, such as Object.prototype or Array.prototype. By polluting the prototype, attackers can introduce malicious properties or methods that affect all objects derived from that prototype.
For example, an attacker can set a property to "__proto__" and add a malicious property with a specific name. This will define the property on all existing objects of the same class in the application, allowing the attacker to control the default values of an object's properties. Successful exploitation of prototype pollution requires a prototype pollution source, which is any input that enables the poisoning of prototype objects with arbitrary properties. A sink, or a JavaScript function that enables arbitrary code execution, is also necessary for a successful attack.
To prevent prototype pollution, developers can use new Set() or new Map() instead of object literals. If objects must be used, they should be created using the Object.create(null) API to ensure they don't inherit from the Object prototype. Additionally, the Object.freeze() and Object.seal() APIs can be used to prevent built-in prototypes from being modified. Removing the "__proto__" property can also help reduce the attack surface and prevent certain prototype pollution attacks.
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Attackers can modify the prototype of an object, affecting all derived objects
Prototype pollution is a critical vulnerability that can occur in JavaScript environments. It allows attackers to modify the prototype of an object, which then affects all objects derived from that prototype. This can have serious consequences, including unauthorized access to data, privilege escalation, and remote code execution.
In JavaScript, objects inherit properties and behaviours from a prototype. Each object has a prototype, and if a property or method is not found on the object itself, JavaScript looks for it in its prototype and then moves up the prototype chain until it reaches the top-level Object.prototype. Attackers can exploit this by modifying the prototype of a commonly used object, such as Object.prototype or Array.prototype. By doing so, they can introduce malicious properties or methods that will affect all objects derived from that prototype.
For example, an attacker can use a technique to pollute the prototype with properties that are used by the application or any imported libraries. They can inject a property with a key like "__proto__" along with arbitrary nested properties. Due to the special meaning of "__proto__" in JavaScript, the merge operation may assign these nested properties to the object's prototype instead of the target object itself. As a result, all objects in the JavaScript runtime will inherit this property unless they already have a property with a matching key.
To protect against prototype pollution, developers can use new Set() or new Map() instead of object literals. If objects must be used, they should be created using the Object.create(null) API to ensure they don't inherit from the Object prototype. Additionally, the Object.freeze() and Object.seal() APIs can be used to prevent built-in prototypes from being modified. It's also important to strictly control parameters and use a whitelist of expected values to prevent problems like massive assignments.
By understanding and addressing prototype pollution vulnerabilities, developers can ensure the security and integrity of their JavaScript applications.
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Attackers can control default values of an object's properties, tampering with application logic
Prototype pollution is a vulnerability that occurs in JavaScript environments, allowing attackers to modify the prototype of an object and thereby affect all objects derived from it. This is an injection attack that targets JavaScript runtimes, where an attacker can control the default values of an object's properties, allowing them to tamper with the logic of the application.
JavaScript objects inherit properties and behaviours from a prototype. If a property or method is not found on the object itself, JavaScript looks for it in its prototype and then moves up the prototype chain until it reaches the top-level Object.prototype. Attackers can modify commonly used objects, such as Object.prototype or Array.prototype, and introduce malicious properties or methods that affect all derived objects. This is known as "polluting the prototype".
By polluting the prototype, attackers can manipulate the behaviour of JavaScript programs. They can add or overwrite methods or properties to perform actions such as data theft, code execution, or denial of service attacks. For example, they might override the toString function with a meaningless value, causing the API to crash. Attackers can also leverage other components (gadgets) loaded in the same context to initiate complex attacks, escalate privileges, or gain access to sensitive information.
To prevent prototype pollution, developers can use new Set() or new Map() instead of object literals. If objects are necessary, they should be created using the Object.create(null) API to ensure they don't inherit from the Object prototype. Additionally, the Object.freeze() and Object.seal() APIs can prevent built-in prototypes from being modified, although this may break the application if the libraries modify the built-in prototypes. Schema validation can also help, ensuring that unneeded attributes are rejected.
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Prototype pollution vulnerabilities can be exploited on both the server and client sides
Prototype pollution is an injection attack that targets JavaScript runtimes. It is a critical vulnerability that can allow attackers to manipulate an application's JavaScript objects and properties, leading to serious security issues. This vulnerability arises when a JavaScript function merges an object containing user-controllable properties with an existing object, without sanitizing the keys. This enables an attacker to inject a property with a key like "__proto__" and arbitrary nested properties. As a result, malicious properties or methods can be introduced, affecting all objects derived from that prototype.
JavaScript objects inherit properties and behaviours from a prototype. If a property or method is not found on the object itself, JavaScript searches for it in its prototype and then moves up the prototype chain until it reaches the top-level "Object.prototype". By exploiting this mechanism, attackers can modify the prototype of commonly used objects, such as "Object.prototype" or "Array.prototype", and manipulate the behaviour of JavaScript programs. This can lead to data theft, code execution, or denial of service attacks.
To protect against prototype pollution, developers can use new Set() or new Map() instead of object literals. If objects are necessary, the "Object.create(null)" API ensures they don't inherit from the Object prototype. Additionally, Object.freeze() and Object.seal() can prevent built-in prototypes from being modified. Robust websites can also set the prototype to null, preventing any inheritance of properties.
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Libraries vulnerable to prototype pollution include jQuery, lodash, express, minimist, and hoek
Prototype pollution is a critical vulnerability that can allow attackers to manipulate a JavaScript application's objects and properties, thereby leading to serious security issues such as unauthorized access to data, privilege escalation, and even remote code execution. It is an injection attack that targets JavaScript runtimes, where an attacker can control the default values of an object's properties. By polluting the prototype, attackers can manipulate the behaviour of JavaScript programs in unintended ways, such as by adding or overwriting methods or properties to perform actions like data theft, code execution, or denial of service attacks.
To prevent prototype pollution, developers can use new Set() or new Map() instead of object literals. Objects should be created using the Object.create(null) API to ensure they don't inherit from the Object prototype. The Object.freeze() and Object.seal() APIs can also be used to prevent built-in prototypes from being modified. Schema validation can be used to ensure that JSON data contains all expected attributes with the appropriate types, and unneeded attributes should be rejected. Additionally, always sanitize untrusted input when recursively setting nested properties, and use libraries like Snyk Advisor to decide which libraries to trust.
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