---
id: "CVE-2021-21166"
kind: "vulnerability"
aliases: ["CVE-2021-21166"]
title: "Google Chromium: Google Chromium Race Condition Vulnerability"
severity: "high"
cvss: 8.8
epss: 0.24027
exploited: true
status: "open"
category: "runtime"
products: [{"name": "Google Chromium", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["browser-users", "chromium", "exploited", "google-chrome", "microsoft-edge", "opera", "runtime"]
not_affected_if: ["fully-patched-browser"]
published_at: "2021-03-09T18:15:16+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-21166", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-21166", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-21166", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Google Chromium: Google Chromium Race Condition Vulnerability

A race condition in Chromium's code lets a remote attacker corrupt heap memory using a specially crafted HTML page. Successful exploitation can give an attacker code execution in the browser, and the flaw is listed as exploited in the wild.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Google Chromium affected ? fixed ?

## How to check

Open chrome://version (or edge://version, opera://about) and compare the version to the fixed release in the vendor advisory; unknown for the exact fixed version in these sources.

## Fix

Update Chrome, Edge, Opera, or any other Chromium-based browser to the vendor's patched release. Apply vendor updates per CISA instructions.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-21166
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-21166
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-21166

## From the sources

Google Chromium contains a race condition vulnerability that allows a remote attacker to potentially exploit heap corruption via a crafted HTML page. This vulnerability could affect multiple web browsers that utilize Chromium, including, but not limited to, Google Chrome, Microsoft Edge, and Opera.

CISA required action: Apply updates per vendor instructions.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_