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In this case, if the attacker pollutes they are likely to be able to leverage this in order to execute code.
Test gotomeeting code#
Remote code execution is generally only possible in cases where the codebase evaluates a specific attribute of an object, and then executes that evaluation.įor example: eval(someobject.someattr). In this case, the code fails and is likely to cause a denial of service.įor example: if an attacker pollutes by defining it as an integer, if the codebase at any point was reliant on someobject.toString() it would fail. The attacker pollutes and alters its state to an unexpected value such as Int or Object. There are a few methods by which Prototype Pollution can be manipulated: TypeĭoS occurs when Object holds generic functions that are implicitly called for various operations (for example, toString and valueOf). myValue is then assigned to the prototype of the class of the object. If the attacker can control the value of “path”, they can set this value to _proto_.myValue. The function that is generally affected contains this signature: theFunction(object, path, value) There are a few JavaScript libraries that use an API to define property values on an object based on a given path. Lodash and Hoek are examples of libraries susceptible to recursive merge attacks.
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Properties are then copied on the Object prototype.Ĭlone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge(,source).
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When the source object contains a property named _proto_ defined with fineProperty(), the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. If property exists and is an object on both the target and the source The logic of a vulnerable recursive merge function follows the following high-level model: merge (target, source) There are two main ways in which the pollution of prototypes occurs: When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. JavaScript allows all Object attributes to be altered, including their magical attributes such as _proto_, constructor and prototype. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. Prototype Pollution is a vulnerability affecting JavaScript. (While untrusted schemas are recommended against, the worst case of an untrusted schema should be a denial of service, not execution of code.) Details A carefully crafted JSON schema could be provided that allows execution of other code by prototype pollution. Affected versions of this package are vulnerable to Prototype Pollution.