{"id":"CVE-2021-21166","kind":"vulnerability","aliases":["CVE-2021-21166"],"related":[],"title":"Google Chromium: Google Chromium Race Condition Vulnerability","description":"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.\n\nCISA required action: Apply updates per vendor instructions.","summary":"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.","severity":"high","cvss":8.8,"epss":0.24027,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","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"],"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.","status":"open","published_at":"2021-03-09T18:15:16+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:39:34+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"runtime","confidence":0.7,"triage":{"at":"2026-10-23T21:39:34Z","model":"claude-haiku-5-5","output":{"fix":"Update Chrome, Edge, Opera, or any other Chromium-based browser to the vendor's patched release. Apply vendor updates per CISA instructions.","reach":"internet","impact":"high","summary":"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.","category":"runtime","who_cares":["chromium","google-chrome","microsoft-edge","opera","browser-users"],"confidence":0.7,"needs_auth":"no","worst_case":"Attacker runs code in the browser via a malicious web page","analyst_note":"Confirm the fixed Chromium version and patch date from the Chrome Releases blog or the NVD entry for CVE-2021-21166, since the sources give no version range.","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.","needs_analyst":true,"not_affected_if":["fully-patched-browser"],"user_interaction":"yes","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000501,"input_tokens":2871,"output_tokens":428,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':9A,12A '-21166':10A,13A 'action':115C 'affect':95C 'allow':78C 'appli':116C 'attack':39B,54B,81C 'browser':17B,59B,98C 'browser-us':16B 'chrome':23B,108C 'chromium':2A,4A,15A,19B,33B,71C,101C 'cisa':113C 'code':35B,55B 'condit':6A,31B,75C 'contain':72C 'corrupt':40B,86C 'could':94C 'craft':46B,89C 'cve':8A,11A 'edg':26B,110C 'execut':56B 'exploit':20B,50B,66B,84C 'flaw':62B 'give':52B 'googl':1A,3A,22B,70C,107C 'google':14A 'google-chrom':21B 'heap':41B,85C 'html':47B,90C 'includ':102C 'instruct':120C 'let':36B 'limit':105C 'list':64B 'memori':42B 'microsoft':25B,109C 'microsoft-edg':24B 'multipl':96C 'opera':27B,112C 'page':48B,91C 'per':118C 'potenti':83C 'race':5A,30B,74C 'remot':38B,80C 'requir':114C 'runtim':28B 'special':45B 'success':49B 'updat':117C 'use':43B 'user':18B 'util':100C 'vendor':119C 'via':87C 'vulner':7A,76C,93C 'web':97C 'wild':69B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-03-09T18:15:16+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","cvss_by":"nvd@nist.gov","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-21166","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-21166","severity":null,"published_at":"2021-11-03T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:53+00:00","fetched_at":"2026-10-25T15:39:44+00:00","note":null},{"source":"epss","external_id":"CVE-2021-21166","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-21166","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-23T19:13:44+00:00","fetched_at":"2026-10-23T19:13:44+00:00","note":null},{"source":"nvd","external_id":"CVE-2021-21166","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21166","severity":null,"published_at":"2021-03-09T18:15:16+00:00","modified_at":"2026-06-17T03:34:57+00:00","first_seen_at":"2026-10-23T21:57:35+00:00","fetched_at":"2026-10-23T21:57:35+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}