{"id":"CVE-2021-1871","kind":"vulnerability","aliases":["CVE-2021-1871"],"related":[],"title":"Apple iOS, iPadOS, and macOS: Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability","description":"Apple iOS, iPadOS, and macOS WebKit contain an unspecified logic vulnerability that allows a remote attacker to execute code. 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":"A logic flaw in WebKit, the browser engine used by Safari and Apple's iOS, iPadOS and macOS, lets a remote attacker run code. Any app that parses HTML with WebKit can be hit, and CISA lists it as actively exploited.","severity":"critical","cvss":9.8,"epss":0.07002,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Apple iOS, iPadOS, and macOS","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["apps-with-embedded-webview","exploited","ios","ipados","macos","safari","vendor","webkit"],"not_affected_if":["fully-patched-devices"],"how_to_check":"Check the device OS version under Settings > General > About (iOS/iPadOS) or About This Mac (macOS) and compare it with the Apple security release that fixed CVE-2021-1871.","fix":"Update iOS, iPadOS and macOS to a release that includes the WebKit fix for CVE-2021-1871, per Apple's security notes.","status":"open","published_at":"2021-04-02T19:15:20+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:37:05+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"vendor","confidence":0.7,"triage":{"at":"2026-10-23T21:37:05Z","model":"claude-haiku-5-5","output":{"fix":"Update iOS, iPadOS and macOS to a release that includes the WebKit fix for CVE-2021-1871, per Apple's security notes.\nunknown","reach":"internet","impact":"high","summary":"A logic flaw in WebKit, the browser engine used by Safari and Apple's iOS, iPadOS and macOS, lets a remote attacker run code. Any app that parses HTML with WebKit can be hit, and CISA lists it as actively exploited.","category":"vendor","who_cares":["ios","ipados","macos","safari","webkit","apps-with-embedded-webview"],"confidence":0.7,"needs_auth":"no","worst_case":"Attacker runs code on the device after a user loads hostile web content.","analyst_note":"Find Apple's security content page for the release that fixed CVE-2021-1871 to confirm the fixed versions; the sources give no affected or fixed version numbers.","how_to_check":"Check the device OS version under Settings > General > About (iOS/iPadOS) or About This Mac (macOS) and compare it with the Apple security release that fixed CVE-2021-1871.\nunknown","needs_analyst":true,"not_affected_if":["fully-patched-devices"],"user_interaction":"yes","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000518,"input_tokens":2914,"output_tokens":453,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-1871':18A,21A '-2021':17A,20A 'action':129C 'activ':78B 'allow':92C 'and':25A 'app':28B,64B 'appl':1A,6A,51B,80C,113C,118C 'apple':22A 'appli':130C 'apps-with-embedded-webview':27B 'attack':60B,95C 'browser':45B 'cisa':74B,127C 'code':13A,62B,98C 'contain':86C 'could':101C 'cve':16A,19A 'embed':30B 'engin':46B 'execut':14A,97C 'exploit':32B,79B 'flaw':41B 'hit':72B 'html':67B,103C,125C 'impact':102C 'includ':108C 'instruct':134C 'io':2A,7A,33B,53B,81C 'ios':23A 'ipado':3A,8A,34B,54B,82C 'ipados':24A 'let':57B 'limit':111C 'list':75B 'logic':40B,89C 'maco':5A,10A,35B,56B,84C 'macos':26A 'non':117C 'non-appl':116C 'pars':66B 'parser':104C 'per':132C 'process':126C 'product':119C 'reli':121C 'remot':12A,59B,94C 'requir':128C 'run':61B 'safari':36B,49B,114C 'unspecifi':88C 'updat':131C 'use':47B,106C 'vendor':37B,133C 'vulner':15A,90C,100C 'webkit':11A,38B,43B,69B,85C,107C,123C 'webview':31B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-04-02T19:15:20+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:N/S:U/C:H/I:H/A:H","cvss_by":"nvd@nist.gov","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-1871","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-1871","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":"2026-10-25T15:39:43+00:00","note":null},{"source":"epss","external_id":"CVE-2021-1871","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-1871","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-2021-1871","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-1871","severity":null,"published_at":"2021-04-02T19:15:20+00:00","modified_at":"2026-06-17T03:32:41+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"}