{"id":"CVE-2025-21418","kind":"vulnerability","aliases":["CVE-2025-21418"],"related":[],"title":"Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability","description":"Microsoft Windows Ancillary Function Driver for WinSock contains a heap-based buffer overflow vulnerability that allows for privilege escalation, enabling a local attacker to gain SYSTEM privileges.\n\nCISA required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.","summary":"A heap-based buffer overflow in the Windows Ancillary Function Driver for WinSock (afd.sys) lets a local user escalate privileges. An attacker with a local foothold gets SYSTEM privileges, and CISA lists it as exploited in the wild.","severity":"high","cvss":7.8,"epss":null,"exploited":true,"exploited_at":"2025-02-11T00:00:00+00:00","products":[{"name":"Microsoft Windows","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft windows 10 1607","fixed":["10.0.10240.20915"],"affected":"< 10.0.10240.20915","ecosystem":"vendor"},{"name":"microsoft windows 10 1809","fixed":["10.0.17763.6893"],"affected":"< 10.0.17763.6893","ecosystem":"vendor"},{"name":"microsoft windows 10 21h2","fixed":["10.0.19044.5487"],"affected":"< 10.0.19044.5487","ecosystem":"vendor"},{"name":"microsoft windows 10 22h2","fixed":["10.0.19045.5487"],"affected":"< 10.0.19045.5487","ecosystem":"vendor"},{"name":"microsoft windows 11 22h2","fixed":["10.0.22621.4890"],"affected":"< 10.0.22621.4890","ecosystem":"vendor"},{"name":"microsoft windows 11 23h2","fixed":["10.0.22631.4890"],"affected":"< 10.0.22631.4890","ecosystem":"vendor"},{"name":"microsoft windows 11 24h2","fixed":["10.0.26100.3107"],"affected":"< 10.0.26100.3107","ecosystem":"vendor"},{"name":"microsoft windows server 2008","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft windows server 2008","fixed":[],"affected":"= r2","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":["10.0.14393.7785"],"affected":"< 10.0.14393.7785","ecosystem":"vendor"},{"name":"microsoft windows server 2019","fixed":["10.0.17763.6893"],"affected":"< 10.0.17763.6893","ecosystem":"vendor"},{"name":"microsoft windows server 2022","fixed":["10.0.20348.3148"],"affected":"< 10.0.20348.3148","ecosystem":"vendor"},{"name":"microsoft windows server 2022 23h2","fixed":["10.0.25398.1425"],"affected":"< 10.0.25398.1425","ecosystem":"vendor"},{"name":"microsoft windows server 2025","fixed":["10.0.26100.3107"],"affected":"< 10.0.26100.3107","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","infrastructure","self-hosted","windows"],"not_affected_if":["patched-windows"],"how_to_check":null,"fix":"Apply the Microsoft security update for CVE-2025-21418 (Windows Ancillary Function Driver for WinSock); the specific KB and affected builds are not in the sources.\nCISA says to apply the vendor mitigations or discontinue use of unpatched products.","status":"open","published_at":"2025-02-11T00:00:00+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:52:28+00:00","updated_at":"2026-10-23T22:29:05+00:00","category":"infrastructure","confidence":0.7,"triage":{"at":"2026-10-23T20:52:28Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft security update for CVE-2025-21418 (Windows Ancillary Function Driver for WinSock); the specific KB and affected builds are not in the sources.\nCISA says to apply the vendor mitigations or discontinue use of unpatched products.","reach":"local","impact":"high","summary":"A heap-based buffer overflow in the Windows Ancillary Function Driver for WinSock (afd.sys) lets a local user escalate privileges. An attacker with a local foothold gets SYSTEM privileges, and CISA lists it as exploited in the wild.","category":"infrastructure","who_cares":["windows","self-hosted"],"confidence":0.7,"needs_auth":"yes","worst_case":"Local user gains SYSTEM privileges on the Windows machine","analyst_note":"Find the Microsoft security update guide entry for CVE-2025-21418 to confirm affected Windows builds and the KB number, and check the CISA KEV entry for the required action deadline.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["patched-windows"],"user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000473,"input_tokens":2663,"output_tokens":414,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2025':12A,15A '-21418':13A,16A '10':21A,25A,29A,33A '11':37A,41A,45A '1607':22A '1809':26A '2008':50A,54A '2012':58A,62A '2016':66A '2019':70A '2022':74A,78A '2025':83A '21h2':30A '22h2':34A,38A '23h2':42A,79A '24h2':46A 'action':159C 'afd.sys':104B 'allow':145C 'ancillari':2A,99B,131C 'appli':160C 'attack':112B,152C 'base':93B,140C 'buffer':94B,141C 'cisa':121B,157C 'contain':136C 'cve':11A,14A 'discontinu':166C 'driver':4A,101B,133C 'elev':7A 'enabl':149C 'escal':109B,148C 'exploit':84B,125B 'foothold':116B 'function':3A,100B,132C 'gain':154C 'get':117B 'heap':92B,139C 'heap-bas':91B,138C 'host':88B 'infrastructur':85B 'instruct':164C 'let':105B 'list':122B 'local':107B,115B,151C 'microsoft':17A,19A,23A,27A,31A,35A,39A,43A,47A,51A,55A,59A,63A,67A,71A,75A,80A,129C 'mitig':161C,172C 'overflow':95B,142C 'per':162C 'privileg':9A,110B,119B,147C,156C 'product':170C 'requir':158C 'self':87B 'self-host':86B 'server':49A,53A,57A,61A,65A,69A,73A,77A,82A 'system':118B,155C 'unavail':174C 'use':167C 'user':108B 'vendor':163C 'vulner':10A,143C 'wild':128B 'window':1A,89B,98B,130C 'windows':18A,20A,24A,28A,32A,36A,40A,44A,48A,52A,56A,60A,64A,68A,72A,76A,81A 'winsock':6A,103B,135C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2025-02-11T00:00:00+00:00","kev":{"dateAdded":"2025-02-11","dueDate":"2025-03-04","requiredAction":"Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2025-21418","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2025-21418","severity":null,"published_at":"2025-02-11T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T16:39:46+00:00","note":null},{"source":"nvd","external_id":"CVE-2025-21418","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-21418","severity":null,"published_at":"2025-02-11T18:15:40+00:00","modified_at":"2026-06-17T08:43:19+00:00","first_seen_at":"2026-10-23T22:29:05+00:00","fetched_at":"2026-10-23T22:29:05+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"}