{"id":"CVE-2021-21206","kind":"vulnerability","aliases":["CVE-2021-21206"],"related":[],"title":"Google Chromium Blink: Google Chromium Blink Use-After-Free Vulnerability","description":"Google Chromium Blink contains a use-after-free 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 use-after-free bug in Chromium's Blink rendering engine lets a remote attacker corrupt heap memory by serving a crafted HTML page. Attackers can use this to run code inside the browser when a user visits the page, and CISA lists it as actively exploited.","severity":"high","cvss":8.8,"epss":0.09307,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Google Chromium Blink","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["chrome","chromium","edge","electron","end-users","exploited","opera","runtime"],"not_affected_if":["already-updated-browser"],"how_to_check":"Open chrome://version (or edge://version, opera://version) and compare the Chromium version with the fixed release in the vendor advisory.","fix":"Update Chrome, Edge, Opera or other Chromium-based browsers to the fixed release named in the vendor advisory.\nCISA required action: apply updates per vendor instructions.","status":"open","published_at":"2021-04-26T17:15:08+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:43:33+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"runtime","confidence":0.7,"triage":{"at":"2026-10-23T21:43:33Z","model":"claude-haiku-5-5","output":{"fix":"Update Chrome, Edge, Opera or other Chromium-based browsers to the fixed release named in the vendor advisory.\nCISA required action: apply updates per vendor instructions.","reach":"internet","impact":"high","summary":"A use-after-free bug in Chromium's Blink rendering engine lets a remote attacker corrupt heap memory by serving a crafted HTML page. Attackers can use this to run code inside the browser when a user visits the page, and CISA lists it as actively exploited.","category":"runtime","who_cares":["chrome","edge","opera","chromium","electron","end-users"],"confidence":0.7,"needs_auth":"no","worst_case":"Attacker runs code in the browser after a victim opens a crafted page","analyst_note":"Find the fixed Chromium version for CVE-2021-21206 in the Chrome Releases blog or the CISA KEV entry and add it to fix and how_to_check.","how_to_check":"Open chrome://version (or edge://version, opera://version) and compare the Chromium version with the fixed release in the vendor advisory.\nunknown\nunknown","needs_analyst":true,"not_affected_if":["already-updated-browser"],"user_interaction":"yes","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000511,"input_tokens":2887,"output_tokens":444,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':13A,16A '-21206':14A,17A 'action':127C 'activ':77B 'affect':107C 'allow':90C 'appli':128C 'attack':46B,56B,93C 'blink':3A,6A,20A,40B,81C 'browser':65B,110C 'bug':36B 'chrome':21B,120C 'chromium':2A,5A,19A,22B,38B,80C,113C 'cisa':73B,125C 'code':62B 'contain':82C 'corrupt':47B,98C 'could':106C 'craft':53B,101C 'cve':12A,15A 'edg':23B,122C 'electron':24B 'end':26B 'end-us':25B 'engin':42B 'exploit':28B,78B,96C 'free':10A,35B,87C 'googl':1A,4A,79C,119C 'google':18A 'heap':48B,97C 'html':54B,102C 'includ':114C 'insid':63B 'instruct':132C 'let':43B 'limit':117C 'list':74B 'memori':49B 'microsoft':121C 'multipl':108C 'opera':29B,124C 'page':55B,71B,103C 'per':130C 'potenti':95C 'remot':45B,92C 'render':41B 'requir':126C 'run':61B 'runtim':30B 'serv':51B 'updat':129C 'use':8A,33B,58B,85C 'use-after-fre':7A,32B,84C 'user':27B,68B 'util':112C 'vendor':131C 'via':99C 'visit':69B 'vulner':11A,88C,105C 'web':109C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-04-26T17:15:08+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-2021-21206","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-21206","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":"2026-10-25T11:39:18+00:00","note":null},{"source":"epss","external_id":"CVE-2021-21206","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-21206","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-2021-21206","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21206","severity":null,"published_at":"2021-04-26T17:15:08+00:00","modified_at":"2026-06-17T03:35:02+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"}