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Date: July 7, 2021


Prototype pollution vulnerability in ‘just-safe-set’ versions 1.0.0 through 2.2.1 allows an attacker to cause a denial of service and may lead to remote code execution.


The NPM module `just-safe-set` can be abused by Prototype Pollution vulnerability since the function `set()` does not check for the type of object before assigning value to the property. Due to this flaw an attacker could create a non-existent property or is able to manipulate the property which leads to Denial of Service or potentially Remote code execution.

PoC Details

The `set()` function accepts `obj`, `props`, and `value` as arguments. Due to the absence of validation on the values passed into the ` props` argument, an attacker can supply a malicious value by adjusting the value to include the `__proto__` property. Since there is no validation before assigning the property to check whether the assigned argument is the Object's own property or not, the property `polluted` will be directly assigned to the new object thereby polluting the Object prototype. Later in the code, if there is a check to validate `polluted` the value would be substituted as "Yes! It's Polluted" as it had been polluted.

PoC Code

var justSafeSet = require("just-safe-set")

var obj = {}

console.log("Before : " + {}.polluted);

justSafeSet(obj,'__proto__.polluted','Yes! Its Polluted');

console.log("After : " + {}.polluted);

Affected Environments

1.0.0 through 2.2.1


Upgrade to version 2.2.2

Language: JS

Good to know:


Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')


Improperly Controlled Modification of Dynamically-Determined Object Attributes


Upgrade Version

Upgrade to version 2.2.2

Learn More

Base Score:
Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): High
Integrity (I): High
Availability (A): High
Base Score:
Access Vector (AV): Network
Access Complexity (AC): Low
Authentication (AU): None
Confidentiality (C): Partial
Integrity (I): Partial
Availability (A): Partial
Additional information: