Polyfill.io Supply Chain Attack

The polyfill.js is a popular open-source library that supports older browsers. Thousands of sites embed it using the cdn[.]polyfill[.]io domain. In February 2024, a Chinese company (Funnull) bought the domain and the GitHub account. The company has modified Polyfill.js so malicious code would be inserted into websites that embedded scripts from cdn.polyfill[.]io. Any script adopted from cdn.polyfill[.]io would immediately download malicious code from the Chinese company's site. Some of the known outcomes are:

• user would be redirected to scam sites,
• allows an attacker to steal sensitive data,
• potentially perform code execution.

Given that modern browsers do not require Polyfill, the original polyfill author recommends not to use Polyfill at all. Recommended alternatives are CDN, such as Cloudflare and Fastly.

Detecting the Vulnerability with Qualys:

Qualys is releasing multiple detections to detect content downloaded from the CDN and sites that have been compromised.

References:

Related