Greta Jimenez
Prototype pollution is a vulnerability that has been found in many popular JavaScript libraries, including set-value. It is an injection attack that targets JavaScript runtimes, allowing an attacker to control the default values of an object's properties and tamper with the logic of the application. This can lead to denial of service or, in extreme cases, remote code execution. To fix prototype pollution in set-value, it is recommended to upgrade to version 4.0.1 or higher, as the vulnerability was patched in this release. There are also other methods to prevent prototype pollution, such as freezing the prototype, using schema validation, and avoiding unsafe recursive merge functions.
| Characteristics | Values |
|---|---|
| How prototype pollution works | The attacker controls the default values of an object's properties, allowing them to tamper with the logic of the application. |
| How to prevent it | Only run trusted libraries on your server. Distribute only a compiled executable with an interprocess API. Put your code into a service and only offer access that way. |
| How to fix it | Freeze the prototype using Object.freeze (Object.prototype). Require schema validation of JSON input. Avoid using unsafe recursive merge functions. Use objects without prototypes (e.g., Object.create(null)). Use Map instead of Object. Sanitize untrusted input when recursively setting nested properties. |
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What You'll Learn
Upgrade to set-value 4.0.1
The set-value 4.0.1 upgrade is a critical fix that addresses a high-severity prototype pollution vulnerability in the previous version, set-value 4.0.0. Prototype pollution is a security issue that allows attackers to inject properties into existing JavaScript language construct prototypes, such as objects. This vulnerability can lead to information disclosure, denial of service, or remote code execution.
To fix this issue, the upgrade to set-value 4.0.1 includes a patch that prevents the manipulation of Object attributes, such as __proto__, constructor, and prototype. By freezing the prototype using Object.freeze(Object.prototype), the upgrade ensures that these attributes cannot be altered or overwritten.
In addition to freezing the prototype, the upgrade also recommends implementing schema validation of JSON input and avoiding unsafe recursive merge functions. It suggests considering the use of objects without prototypes, such as Object.create(null), to break the prototype chain and prevent pollution. As a best practice, the use of Map instead of Object is also recommended.
The set-value 4.0.1 upgrade also addresses the issue of many libraries requiring set-value@^2.0.0, which prevented users from upgrading to version 4. To resolve this, a patch version of 2.0.2 was released, completely mitigating the CVE-2021-23440 vulnerability. This allows users to upgrade their local versions while still depending on the older set-value@^2.0.0 libraries.
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Use Object.freeze (Object.prototype)
Prototype pollution is an injection attack that targets JavaScript runtimes. An attacker can control the default values of an object's properties, allowing them to tamper with the logic of the application. This can lead to denial of service or, in extreme cases, remote code execution.
One way to prevent prototype pollution is to use Object.freeze(Object.prototype). This method invokes the Object.freeze() function on the Object.prototype, ensuring that its properties and values cannot be modified, and no new properties can be added. Freezing the prototype is a well-established practice to harden an application against prototype pollution attacks and is generally effective.
However, it's important to note that modifying the Object.prototype is generally discouraged, especially in a shared repository or professional setting. There are alternative approaches to achieve the desired results without modifying the base prototypes.
Additionally, while Object.freeze(Object.prototype) can prevent prototype pollution, it is not the only solution. Other methods include using Object.create(null) to avoid prototypes altogether, sanitizing property keys before merging them into existing objects, and using an allowlist or blocklist to control property keys.
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Require schema validation of JSON input
To fix prototype pollution in set-value, one of the methods is to require schema validation of JSON input. This is because prototype pollution is a vulnerability that allows attackers to inject properties into existing JavaScript language construct prototypes, such as objects.
JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor, and prototype. By manipulating these attributes, attackers can overwrite or pollute a JavaScript application object prototype of the base object by injecting other values.
To prevent this, schema validation of JSON input can be used to ensure that the JSON data adheres to a predefined schema or structure. This helps to validate the input data and ensure that it meets the expected format and data types. By requiring schema validation, you can restrict the ability of attackers to inject malicious payloads or exploit vulnerabilities in your application.
It is important to note that while requiring schema validation of JSON input is a recommended practice, it should be combined with other security measures to effectively mitigate prototype pollution attacks. Regular security updates and patches should also be applied to address known vulnerabilities and reduce the attack surface.
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Avoid unsafe recursive merge functions
Unsafe recursive merge functions can be manipulated by attackers to inject properties into existing JavaScript language construct prototypes, such as objects. This is known as prototype pollution.
To avoid unsafe recursive merge functions, it is recommended to freeze the prototype by using Object.freeze (Object.prototype). This will prevent any changes from being made to the prototype. Additionally, require schema validation of JSON input to ensure that any data being merged into the object is in the expected format and does not contain any malicious code.
It is also suggested to consider using objects without prototypes, such as Object.create(null), which breaks the prototype chain and prevents pollution. As a best practice, use Map instead of Object to reduce the risk of prototype pollution.
By following these guidelines, you can help protect your code from prototype pollution vulnerabilities and ensure the security and integrity of your JavaScript applications.
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Use objects without prototypes
One way to fix prototype pollution in set-value is to use objects without prototypes. This can be done by using Object.create() with a null value as the first argument. Here's an example:
Javascript
Let obj = Object.create(null);
Obj.__proto__ // undefined
Obj.constructor // undefined
In this code snippet, we create an object "obj" using Object.create(null). By passing null as the first argument, we ensure that the created object does not have a prototype. As a result, obj.__proto__ and obj.constructor are undefined, indicating the absence of a prototype. This approach helps to prevent prototype pollution because an object without a prototype cannot be polluted.
Another way to create objects without prototypes is by using Object.create(Object.prototype) with a frozen prototype. Here's an example:
Javascript
Object.freeze(Object.prototype);
Let obj = Object.create(Object.prototype);
In this code, we first freeze the default Object.prototype using Object.freeze(). Then, we create a new object "obj" using Object.create(Object.prototype). By freezing the prototype, we prevent any modifications to its attributes, including prototype pollution.
Using objects without prototypes is a best practice to mitigate prototype pollution. It breaks the prototype chain and prevents the pollution from spreading to other objects. However, it's important to note that objects created without prototypes may not have the expected behaviour or inherit properties from the prototype chain.
In addition to using objects without prototypes, there are other measures to prevent prototype pollution. For example, freezing the prototype of an object using Object.freeze(object) can prevent any modifications to its attributes. Schema validation of JSON input and avoiding unsafe recursive merge functions are also recommended practices to enhance security against prototype pollution attacks.
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Frequently asked questions
Prototype pollution is an injection attack that targets JavaScript runtimes. It allows attackers to control the default values of an object's properties, enabling them to tamper with the logic of the application. This can lead to denial of service or remote code execution.
Prototype pollution in set-value occurs when an attacker manipulates object attributes such as __proto__, constructor, and prototype, to inject and overwrite values in a JavaScript application object prototype.
To prevent prototype pollution, you can freeze the prototype using Object.freeze(Object.prototype). Additionally, always validate the schema of JSON input and avoid using unsafe recursive merge functions. Consider using objects without prototypes, such as Object.create(null), to break the prototype chain.
Prototype pollution vulnerabilities have been found in popular JavaScript libraries, including jQuery, lodash, express, minimist, and hoek. For example, a vulnerability in jQuery affected 74% of all websites at the time of discovery.
To fix prototype pollution in set-value, update to version 4.0.1 or higher, as the vulnerability was patched in this release. Additionally, ensure that you only run trusted libraries on your server and keep your package dependencies up to date.
