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mockjs vulnerable to Prototype Pollution via the Util.extend function

High severity GitHub Reviewed Published Dec 8, 2023 to the GitHub Advisory Database • Updated Dec 17, 2023

Package

npm mockjs (npm)

Affected versions

<= 1.1.0

Patched versions

None

Description

All versions of the package mockjs are vulnerable to Prototype Pollution via the Util.extend function due to missing check if the attribute resolves to the object prototype. By adding or modifying attributes of an object prototype, it is possible to create attributes that exist on every object, or replace critical attributes with malicious ones. This can be problematic if the software depends on existence or non-existence of certain attributes, or uses pre-defined attributes of object prototype (such as hasOwnProperty, toString or valueOf).

User controlled inputs inside the extend() method of the Mock.Handler, Mock.Random, Mock.RE.Handler or Mock.Util, will allow an attacker to exploit this vulnerability.

Workaround

By using a denylist of dangerous attributes, this weakness can be eliminated.

Add the following line in the Util.extend function:

js
js if (["proto", "constructor", "prototype"].includes(name)) continue

js
// src/mock/handler.js
Util.extend = function extend() {
var target = arguments[0] || {},
i = 1,
length = arguments.length,
options, name, src, copy, clone

    if (length === 1) {
        target = this
        i = 0
    }

    for (; i < length; i++) {
        options = arguments[i]
        if (!options) continue

        for (name in options) {
        if (["__proto__", "constructor", "prototype"].includes(name)) continue
            src = target[name]
            copy = options[name]

            if (target === copy) continue
            if (copy === undefined) continue

            if (Util.isArray(copy) || Util.isObject(copy)) {
                if (Util.isArray(copy)) clone = src && Util.isArray(src) ? src : []
                if (Util.isObject(copy)) clone = src && Util.isObject(src) ? src : {}

                target[name] = Util.extend(clone, copy)
            } else {
                target[name] = copy
            }
        }
    }

    return target
}

References

Published by the National Vulnerability Database Dec 8, 2023
Published to the GitHub Advisory Database Dec 8, 2023
Reviewed Dec 8, 2023
Last updated Dec 17, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

EPSS score

0.046%
(18th percentile)

Weaknesses

CVE ID

CVE-2023-26158

GHSA ID

GHSA-mh8j-9jvh-gjf6

Source code

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