Closure JavaScript Library introduced XSS issue in Google Search and potentially other services

A change made months ago in an open-source JavaScript library introduced a cross-site scripting (XSS) vulnerability in Google Search.

The Japanese security researcher Masato Kinugawa discovered an XSS vulnerability in Google Search that was introduced with a change made months ago in an open-source JavaScript library.

The library is named Closure and according to the expert it fails to properly sanitize user input. Closure Library is a powerful, low-level JavaScript library designed for building complex and scalable web applications. It is used by many Google web applications, such as Google Search, Gmail, Google Docs, Google+, Google Maps, and others.

The flaw could be potentially exploited by threat actors to carry out phishing attacks and other malicious activities.

According to an analysis conducted by LiveOverflow, the XSS vulnerability was apparently introduced on September 26, 2018, when a sanitization mechanism was removed after the review of the user interface design.

I never thought I would experience a XSS on Google Search. But @kinugawamasato blew my mind!

This is a video going over the difficulties of sanitizing HTML in JavaScript.https://t.co/T61VJJEuDE pic.twitter.com/EwoM0GaW3o

— LiveOverflow 🔴 (@LiveOverflow) March 31, 2019

The design change was reverted on February 22, 2019, Google confirmed to have quickly addressed the vulnerability shortly after learning of its existence.

The analysis of the comments posted by developers when the change was reverted revealed that the bug was related to an HTML sanitizer. The issue was the root cause of the introduction of an XSS flaw in the Google Web Server (GWS) software.

Experts at LiveOverflow speculated the vulnerability likely affected other Google products that use the Closure library.

LiveOverflow has published a video PoC for the vulnerability:

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Pierluigi Paganini

(SecurityAffairs – XSS, hacking)

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