{"id":"CVE-2021-30666","kind":"vulnerability","aliases":["CVE-2021-30666"],"related":[],"title":"Apple iOS: Apple iOS WebKit Buffer Overflow Vulnerability","description":"Apple iOS WebKit contains a buffer-overflow vulnerability that leads to code execution when processing maliciously crafted web content. This vulnerability could impact HTML parsers that use WebKit, including but not limited to Apple Safari and non-Apple products which rely on WebKit for HTML processing.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Apple iOS WebKit has a buffer overflow that is triggered when the browser engine processes crafted web content. An attacker who gets a victim to load a malicious page can run code on the device.","severity":"high","cvss":8.8,"epss":0.02998,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Apple iOS","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","ios","iphone","safari","vendor","webkit"],"not_affected_if":["up-to-date-ios"],"how_to_check":"Check the iOS version on the device under Settings > General > About; compare it with the fixed release in Apple's security notes (unknown from sources).","fix":"Update iOS to a release that includes the Apple fix for CVE-2021-30666 (exact version unknown from sources); apply updates per vendor instructions as CISA requires.","status":"open","published_at":"2021-09-08T15:15:13+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:34:00+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"vendor","confidence":0.7,"triage":{"at":"2026-10-23T21:34:00Z","model":"claude-haiku-5-5","output":{"fix":"Update iOS to a release that includes the Apple fix for CVE-2021-30666 (exact version unknown from sources); apply updates per vendor instructions as CISA requires.","reach":"internet","impact":"high","summary":"Apple iOS WebKit has a buffer overflow that is triggered when the browser engine processes crafted web content. An attacker who gets a victim to load a malicious page can run code on the device.","category":"vendor","who_cares":["ios","iphone","safari","webkit"],"confidence":0.7,"needs_auth":"no","worst_case":"Attacker runs code on the device after the user loads crafted web content.","analyst_note":"Confirm fixed iOS version and affected range from Apple's security content for CVE-2021-30666; sources do not list it.","how_to_check":"Check the iOS version on the device under Settings > General > About; compare it with the fixed release in Apple's security notes (unknown from sources).","needs_analyst":true,"not_affected_if":["up-to-date-ios"],"user_interaction":"yes","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000479,"input_tokens":2877,"output_tokens":382,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':10A,13A '-30666':11A,14A 'action':108C 'appl':1A,3A,23B,58C,92C,97C 'apple':15A 'appli':109C 'attack':42B 'browser':35B 'buffer':6A,28B,64C 'buffer-overflow':63C 'cisa':106C 'code':54B,70C 'contain':61C 'content':40B,77C 'could':80C 'craft':38B,75C 'cve':9A,12A 'devic':57B 'engin':36B 'execut':71C 'exploit':17B 'get':44B 'html':82C,104C 'impact':81C 'includ':87C 'instruct':113C 'io':2A,4A,18B,24B,59C 'ios':16A 'iphon':19B 'lead':68C 'limit':90C 'load':48B 'malici':50B,74C 'non':96C 'non-appl':95C 'overflow':7A,29B,65C 'page':51B 'parser':83C 'per':111C 'process':37B,73C,105C 'product':98C 'reli':100C 'requir':107C 'run':53B 'safari':20B,93C 'trigger':32B 'updat':110C 'use':85C 'vendor':21B,112C 'victim':46B 'vulner':8A,66C,79C 'web':39B,76C 'webkit':5A,22B,25B,60C,86C,102C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-09-08T15:15:13+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-2021-30666","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-30666","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":"2026-10-25T11:39:17+00:00","note":null},{"source":"epss","external_id":"CVE-2021-30666","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-30666","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-2021-30666","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-30666","severity":null,"published_at":"2021-09-08T15:15:13+00:00","modified_at":"2026-06-17T03:50:39+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"}