Helena Joyce
Prototype pollution is a critical vulnerability that enables attackers to manipulate an application's JavaScript objects and properties. This vulnerability allows threat actors to inject properties into existing JavaScript construct prototypes, compromising the application. It is called prototype pollution because it allows threat actors to inject values that overwrite or corrupt the prototype of a base object. This malicious prototype can then be passed on to many other objects that inherit that prototype. Prototype pollution vulnerabilities may exist on both the server and client sides of a web application, and successful exploitation can lead to serious security issues such as unauthorized access to data, privilege escalation, and remote code execution.
| Characteristics | Values |
|---|---|
| Type of vulnerability | Injection attack |
| Target | JavaScript runtimes |
| Attack vector | Prototype pollution source, sink, exploitable gadget |
| Impact | Denial of service (DoS), privilege escalation, unauthorized access to data, remote code execution (RCE), cross-site scripting (XSS) |
| Mitigation | Use of safe merge functions, removal of proto property, use of new Set() or new Map() instead of object literals, use of Object.freeze() and Object.seal() APIs, use of prototype-free objects, regular updates of libraries, strict control of parameters |
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What You'll Learn
- Prototype pollution is a JavaScript vulnerability
- Attackers inject properties into existing JavaScript construct prototypes
- Prototype pollution vulnerabilities may exist on both the server and client sides
- Exploiting prototype pollution vulnerabilities can be complex
- Prototype pollution vulnerabilities can be mitigated
Prototype pollution is a JavaScript vulnerability
In JavaScript, an object is a collection of pairs that contain keys and their corresponding values. An attacker can inject a property with a key like "__proto__" along with arbitrary nested properties. Due to the special meaning of "__proto__" in a JavaScript context, the merge operation may assign the nested properties to the object's prototype instead of the target object itself. This enables attackers to pollute the prototype with properties containing harmful values, which may subsequently be used by the application in a dangerous way.
A successful prototype pollution attack requires three key components: a prototype pollution source, a sink, and an exploitable gadget. The source is any input that enables attackers to poison prototype objects with arbitrary properties. A sink is a JavaScript function or DOM element that enables arbitrary code execution. A gadget is any property passed into a sink without proper filtering or sanitization.
The impact of a prototype pollution attack can vary depending on the application logic and implementation. It can result in denial of service (DoS), unauthorized access to data, privilege escalation, cross-site scripting (XSS), or remote code execution (RCE). Server-side exploitation of prototype pollution vulnerabilities can have a more severe impact than client-side attacks. However, the attack surface on the client side is much greater due to the universal use of JavaScript by modern browsers.
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Attackers inject properties into existing JavaScript construct prototypes
Prototype pollution is a vulnerability that enables attackers to exploit JavaScript runtimes. It occurs when attackers inject properties into existing JavaScript construct prototypes, overwriting or polluting the "prototype" of a base object. This malicious prototype can then be inherited by many other objects, allowing attackers to control the default values of the object's properties and tamper with the application's logic. This can lead to serious consequences such as denial of service (DoS) or remote code execution (RCE).
JavaScript can run on both the client-side and server-side of a web application, which is why prototype pollution vulnerabilities may exist on both sides. Prototype attacks can vary in scope and damage depending on the application logic and implementation. For example, a prototype pollution attack can enable threat actors to perform a DoS attack against a targeted user or on the web server hosting the application. It can also result in unexpected behaviours, such as logic not executing as intended, or provide a starting point for additional attacks by allowing threat actors to leverage other components loaded in the same context.
Client-side exploitation of prototype pollution vulnerabilities can result in cross-site scripting (XSS) attacks, where threat actors look for a gadget that relies on the property of an object susceptible to pollution. If the object interacts with the page's document object model (DOM), attackers can trigger client-side JavaScript code execution. Server-side exploitation, on the other hand, occurs when attackers modify the Object prototype's properties using gadgets located in the application context. This can have a more severe impact than client-side attacks as the modified JavaScript runtime objects are executed on the server.
Exploiting prototype pollution vulnerabilities can be complex and typically requires a deep analysis of the application logic to determine the attack's impact. A successful exploitation of prototype pollution requires a prototype pollution source, which is any input that enables the injection of arbitrary properties into global object prototypes. This can be achieved by manipulating the __proto__ attribute, which is present in all JavaScript objects due to the ECMAScript 2015, 6th Edition specification released by the European Computer Manufacturers Association (ECMA).
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Prototype pollution vulnerabilities may exist on both the server and client sides
Prototype pollution is a JavaScript vulnerability that enables attackers to inject properties into existing JavaScript construct prototypes, compromising the application. This vulnerability allows attackers to control the default values of an object's properties, which can lead to serious security issues such as unauthorized access to data, privilege escalation, and remote code execution.
JavaScript can run on both the client-side and server-side of a web application, which is why prototype pollution vulnerabilities may exist on both sides. Prototype attacks can vary in scope and damage, depending on the application logic and implementation. For example, a successful prototype pollution attack on the client-side can result in cross-site scripting (XSS) attacks, where threat actors look for a gadget that relies on the property of an object susceptible to pollution. If the object interacts with the page's document object model (DOM), attackers can trigger client-side JavaScript code execution.
On the other hand, server-side exploitation occurs when attackers modify the Object prototype's properties using gadgets located in the application context. This can lead to more severe impacts than client-side attacks, as the modified JavaScript runtime objects are executed on the server. For example, server-side prototype pollution can result in remote code execution, where an attacker sends a malicious payload to the backend server, and an unsafe merge function recursively merges that payload with a backend object.
To protect against prototype pollution vulnerabilities, developers can use tools such as Imperva Runtime Application Self-Protection (RASP) and Imperva Web Application Firewall (WAF). Additionally, it is recommended to use new Set() or new Map() instead of object literals, and to create objects using the Object.create(null) API to ensure they don't inherit from the Object prototype. Regularly updating libraries and dependencies can also help mitigate the risks associated with prototype pollution vulnerabilities.
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Exploiting prototype pollution vulnerabilities can be complex
To successfully exploit prototype pollution, several key components are required:
- A prototype pollution source: This is any input that enables attackers to inject arbitrary properties into prototype objects.
- A sink: A JavaScript function or DOM element that enables arbitrary code execution.
- An exploitable gadget: Any property passed into a sink without proper filtering or sanitization.
Detecting and exploiting prototype pollution vulnerabilities require a good understanding of how JavaScript works and how objects are instantiated. It is also important to know the specific measures to implement to counter these attacks. For example, using tools like the Burp extension, DOM Invader, which can automatically identify client-side prototype pollution by finding the source and sink of the injection.
Additionally, there are techniques to detect and exploit this vulnerability without causing a denial of service on the application. This includes modifying the global prototype, changing the data encoding, and limiting the number of parameters in a request. Regularly updating libraries and dependencies can also help mitigate the risks associated with prototype pollution vulnerabilities.
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Prototype pollution vulnerabilities can be mitigated
Prototype pollution is a JavaScript vulnerability that allows attackers to inject properties into existing JavaScript construct prototypes, compromising the application. This vulnerability can be exploited on both the server and client sides, leading to various attacks such as cross-site scripting (XSS) and remote code execution. However, there are several ways to mitigate prototype pollution vulnerabilities and enhance the security of applications.
One approach to mitigating prototype pollution is to utilize tools such as the Imperva Runtime Application Self-Protection (RASP) and the Imperva Web Application Firewall (WAF). RASP provides real-time attack detection and prevention, blocking external attacks and injections. On the other hand, WAF offers world-class analysis of web traffic to prevent attacks proactively. Additionally, API Security and Advanced Bot Protection from Imperva can safeguard APIs and prevent business logic attacks, respectively.
Another mitigation strategy is to employ the Object.create() method when creating new objects instead of using object literals or the object constructor. By passing null as the first argument to Object.create(), the created object will not have a prototype, making it immune to prototype pollution. Furthermore, the Object.freeze() method in JavaScript can be utilized to prevent any changes to the attributes of an object, including the prototype, by freezing it.
To enhance security, developers can also use popular open-source libraries like lodash, which has a strong track record of promptly addressing security issues. Snyk Advisor is another valuable resource that provides insights into the security, community support, and popularity of different packages. Additionally, vulnerability scanners, such as Snyk, can notify developers about new vulnerabilities in their libraries, making it easier to stay ahead of potential exploits.
While mitigating prototype pollution attacks is challenging, it is crucial to develop code with this security vulnerability in mind. This includes implementing safe merge functions that prevent malicious inputs from affecting prototypes and ensuring proper sanitation and validation of inputs to prevent prototype pollution attacks. By adopting these measures, developers can proactively protect their applications and reduce the impact of prototype pollution vulnerabilities.
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Frequently asked questions
Prototype pollution is a JavaScript vulnerability that enables attackers to inject properties into existing JavaScript construct prototypes, compromising the application. This vulnerability allows attackers to manipulate an application's JavaScript objects and properties, leading to unauthorized access to data, privilege escalation, and remote code execution.
Prototype pollution vulnerabilities arise when a JavaScript function recursively merges an object with user-controllable properties into an existing object without sanitizing the keys. Attackers can inject properties with keys like "__proto__" and arbitrary nested properties. Due to the special meaning of "__proto__" in JavaScript, nested properties may be assigned to the object's prototype, allowing attackers to pollute it with harmful values.
Prototype pollution can lead to significant security issues, including unauthorized access to data, privilege escalation, Denial of Service (DoS), and remote code execution (RCE). In client-side JavaScript, it commonly results in DOM cross-site scripting (XSS) attacks, while server-side prototype pollution can have more severe impacts, such as remote code execution.
To mitigate prototype pollution vulnerabilities, developers can use new Set() or new Map() instead of object literals. They can also use Object.freeze() and Object.seal() APIs to prevent built-in prototypes from being modified. Regularly updating libraries and dependencies helps reduce the risk of exploitation. Tools like Imperva Runtime Application Self-Protection (RASP) and Web Application Firewall (WAF) can also detect and prevent prototype pollution attacks.
