CVE-2023-26158 mockjs vulnerable to Prototype Pollution via the Util.extend function

What is CVE-2023-26158?

CVE-2023-26158 is a high-severity vulnerability in mockjs, published on 8 Dec 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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 }

Weakness: CWE-1321

Which versions are affected by CVE-2023-26158?

2 open source packages ship an affected version, including mockjs. It affects 1 product.

Products include Mockjs Mock.js.

How do I fix CVE-2023-26158?

No fix has been published for CVE-2023-26158 yet. Limit exposure of the affected software until one is available.

Is CVE-2023-26158 being exploited?

There is no known exploitation of CVE-2023-26158 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-mh8j-9jvh-gjf6.