{"id":"CVE-2021-26411","kind":"vulnerability","aliases":["CVE-2021-26411"],"related":[],"title":"Microsoft Internet Explorer: Microsoft Internet Explorer Memory Corruption Vulnerability","description":"Microsoft Internet Explorer contains an unspecified vulnerability that allows for memory corruption.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Microsoft Internet Explorer has a memory corruption flaw that attackers have used in real attacks, and CISA lists it as known exploited. A successful exploit can let an attacker run code on the victim's machine.","severity":"high","cvss":8.8,"epss":0.81667,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Microsoft Internet Explorer","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","internet-explorer","ransomware","runtime","windows"],"not_affected_if":["no-ie-installed"],"how_to_check":"Run 'reg query \"HKLM\\SOFTWARE\\Microsoft\\Internet Explorer\" /v svcVersion' or check Internet Explorer's version under Help > About; unknown for other checks.","fix":"Apply the Microsoft security update for CVE-2021-26411 per vendor instructions; unknown for the exact KB number in these sources.","status":"open","published_at":"2021-03-11T16:15:13+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:39:31+00:00","updated_at":"2026-10-23T21:57:34+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-23T21:39:31Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft security update for CVE-2021-26411 per vendor instructions; unknown for the exact KB number in these sources.","reach":"internet","impact":"high","summary":"Microsoft Internet Explorer has a memory corruption flaw that attackers have used in real attacks, and CISA lists it as known exploited. A successful exploit can let an attacker run code on the victim's machine.","category":"runtime","who_cares":["internet-explorer","windows"],"confidence":0.6,"needs_auth":"no","worst_case":"Attacker runs code on the victim's machine through a crafted page.","analyst_note":"Confirm exact affected IE/Windows builds and KB numbers from the Microsoft advisory for CVE-2021-26411.","how_to_check":"Run 'reg query \"HKLM\\SOFTWARE\\Microsoft\\Internet Explorer\" /v svcVersion' or check Internet Explorer's version under Help > About; unknown for other checks.","needs_analyst":true,"not_affected_if":["no-ie-installed"],"user_interaction":"yes","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000485,"input_tokens":2828,"output_tokens":405,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':11A,14A '-26411':12A,15A 'action':76C 'allow':70C 'appli':77C 'attack':35B,40B,54B 'cisa':42B,74C 'code':56B 'contain':65C 'corrupt':8A,32B,73C 'cve':10A,13A 'exploit':19B,47B,50B 'explor':3A,6A,22B,28B,64C 'explorer':18A 'flaw':33B 'instruct':81C 'internet':2A,5A,17A,21B,27B,63C 'internet-explor':20B 'known':46B 'let':52B 'list':43B 'machin':61B 'memori':7A,31B,72C 'microsoft':1A,4A,16A,26B,62C 'per':79C 'ransomwar':23B 'real':39B 'requir':75C 'run':55B 'runtim':24B 'success':49B 'unspecifi':67C 'updat':78C 'use':37B 'vendor':80C 'victim':59B 'vulner':9A,68C 'window':25B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-03-11T16:15:13+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-26411","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-26411","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":"2026-10-25T10:39:08+00:00","note":null},{"source":"epss","external_id":"CVE-2021-26411","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-26411","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-23T19:13:43+00:00","fetched_at":"2026-10-23T19:13:43+00:00","note":null},{"source":"nvd","external_id":"CVE-2021-26411","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-26411","severity":null,"published_at":"2021-03-11T16:15:13+00:00","modified_at":"2026-10-01T21:17:16+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","fetched_at":"2026-10-23T21:57:34+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"}