{"id":"CVE-2026-21513","kind":"vulnerability","aliases":["CVE-2026-21513"],"related":[],"title":"Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a…","description":"Microsoft MSHTML Framework contains a protection mechanism failure vulnerability that could allow an unauthorized attacker to bypass a security feature over a network.\n\nCISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","summary":"Microsoft MSHTML Framework, the browser rendering engine used by Windows, has a protection mechanism failure that lets an unauthenticated attacker bypass a security feature over the network. CISA lists it as actively exploited in the wild.","severity":"high","cvss":8.8,"epss":null,"exploited":true,"exploited_at":"2026-02-10T00:00:00+00:00","products":[{"name":"Microsoft Windows","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft windows 10 1607","fixed":["10.0.14393.8868"],"affected":"< 10.0.14393.8868","ecosystem":"vendor"},{"name":"microsoft windows 10 1809","fixed":["10.0.17763.8389"],"affected":"< 10.0.17763.8389","ecosystem":"vendor"},{"name":"microsoft windows 10 21h2","fixed":["10.0.19044.6937"],"affected":"< 10.0.19044.6937","ecosystem":"vendor"},{"name":"microsoft windows 10 22h2","fixed":["10.0.19045.6937"],"affected":"< 10.0.19045.6937","ecosystem":"vendor"},{"name":"microsoft windows 11 23h2","fixed":["10.0.22631.6649"],"affected":"< 10.0.22631.6649","ecosystem":"vendor"},{"name":"microsoft windows 11 24h2","fixed":["10.0.26100.7781"],"affected":"< 10.0.26100.7781","ecosystem":"vendor"},{"name":"microsoft windows 11 25h2","fixed":["10.0.26200.7781"],"affected":"< 10.0.26200.7781","ecosystem":"vendor"},{"name":"microsoft windows server 2012","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft windows server 2012","fixed":[],"affected":"= r2","ecosystem":"vendor"},{"name":"microsoft windows server 2016","fixed":["10.0.14393.8868"],"affected":"< 10.0.14393.8868","ecosystem":"vendor"},{"name":"microsoft windows server 2019","fixed":["10.0.17763.8389"],"affected":"< 10.0.17763.8389","ecosystem":"vendor"},{"name":"microsoft windows server 2022","fixed":["10.0.20348.4711"],"affected":"< 10.0.20348.4711","ecosystem":"vendor"},{"name":"microsoft windows server 2022 23h2","fixed":["10.0.25398.2149"],"affected":"< 10.0.25398.2149","ecosystem":"vendor"},{"name":"microsoft windows server 2025","fixed":["10.0.26100.32313"],"affected":"< 10.0.26100.32313","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","microsoft-windows","mshtml","other","windows"],"not_affected_if":[],"how_to_check":null,"fix":"Apply the Microsoft security update for CVE-2026-21513 per vendor instructions; if no mitigation is available, discontinue use of the affected product (per CISA guidance).","status":"open","published_at":"2026-02-10T00:00:00+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:42:21+00:00","updated_at":"2026-10-23T23:44:51+00:00","category":"other","confidence":0.6,"triage":{"at":"2026-10-23T20:42:21Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft security update for CVE-2026-21513 per vendor instructions; if no mitigation is available, discontinue use of the affected product (per CISA guidance).\nunknown","reach":"network","summary":"Microsoft MSHTML Framework, the browser rendering engine used by Windows, has a protection mechanism failure that lets an unauthenticated attacker bypass a security feature over the network. CISA lists it as actively exploited in the wild.","category":"other","who_cares":["windows","microsoft-windows","mshtml"],"confidence":0.6,"needs_auth":"unknown","worst_case":"Attacker bypasses a Windows security feature remotely, enabling further compromise of the machine.","analyst_note":"Sources do not name affected Windows builds, the fixed update, or the exact mitigation; check Microsoft's MSRC advisory for CVE-2026-21513 and the CISA KEV entry.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":[],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000448,"input_tokens":2539,"output_tokens":389,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-01':159C '-2026':17A,20A '-21513':18A,21A '10':26A,30A,34A,38A '11':42A,46A,50A '1607':27A '1809':31A '2012':55A,59A '2016':63A '2019':67A '2022':71A,75A '2025':80A '21h2':35A '22':158C '22h2':39A '23h2':43A,76A '24h2':47A '25h2':51A 'action':149C 'activ':119B 'allow':7A,135C 'appli':150C 'applic':156C 'attack':10A,107B,138C 'bod':157C 'browser':92B 'bypass':12A,108B,140C 'cisa':115B,147C 'cloud':162C 'contain':127C 'could':134C 'cve':16A,19A 'discontinu':165C 'engin':94B 'exploit':81B,120B 'failur':3A,102B,131C 'featur':15A,111B,143C 'follow':155C 'framework':6A,90B,126C 'guidanc':160C 'instruct':154C 'let':104B 'list':116B 'mechan':2A,101B,130C 'microsoft':22A,24A,28A,32A,36A,40A,44A,48A,52A,56A,60A,64A,68A,72A,77A,83B,88B,124C 'microsoft-window':82B 'mitig':151C,171C 'mshtml':5A,85B,89B,125C 'network':114B,146C 'per':152C 'product':169C 'protect':1A,100B,129C 'render':93B 'requir':148C 'secur':14A,110B,142C 'server':54A,58A,62A,66A,70A,74A,79A 'servic':163C 'unauthent':106B 'unauthor':9A,137C 'unavail':173C 'use':95B,166C 'vendor':153C 'vulner':132C 'wild':123B 'window':84B,87B,97B 'windows':23A,25A,29A,33A,37A,41A,45A,49A,53A,57A,61A,65A,69A,73A,78A","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2026-02-10T00:00:00+00:00","kev":{"dateAdded":"2026-02-10","dueDate":"2026-03-03","requiredAction":"Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","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":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2026-21513","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-21513","severity":null,"published_at":"2026-02-10T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T19:35:20+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-21513","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-21513","severity":null,"published_at":"2026-02-10T18:16:33+00:00","modified_at":"2026-06-17T10:18:45+00:00","first_seen_at":"2026-10-23T23:44:51+00:00","fetched_at":"2026-10-23T23:44:51+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"}