{"id":"CVE-2025-21335","kind":"vulnerability","aliases":["CVE-2025-21335"],"related":[],"title":"Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability","description":"Microsoft Windows Hyper-V NT Kernel Integration VSP contains a use-after-free vulnerability that allows 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 use-after-free bug in the Windows Hyper-V NT Kernel Integration VSP lets a local user corrupt kernel memory. An attacker who already has a local account can gain SYSTEM privileges, and CISA reports it is being exploited in the wild.","severity":"high","cvss":7.8,"epss":null,"exploited":true,"exploited_at":"2025-01-14T00:00:00+00:00","products":[{"name":"Microsoft Windows","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft windows 10 21h2","fixed":["10.0.19044.5371"],"affected":"< 10.0.19044.5371","ecosystem":"vendor"},{"name":"microsoft windows 10 22h2","fixed":["10.0.19045.5371"],"affected":"< 10.0.19045.5371","ecosystem":"vendor"},{"name":"microsoft windows 11 22h2","fixed":["10.0.22621.4751"],"affected":"< 10.0.22621.4751","ecosystem":"vendor"},{"name":"microsoft windows 11 23h2","fixed":["10.0.22631.4751"],"affected":"< 10.0.22631.4751","ecosystem":"vendor"},{"name":"microsoft windows 11 24h2","fixed":["10.0.26100.2894"],"affected":"< 10.0.26100.2894","ecosystem":"vendor"},{"name":"microsoft windows server 2022 23h2","fixed":["10.0.25398.1369"],"affected":"< 10.0.25398.1369","ecosystem":"vendor"},{"name":"microsoft windows server 2025","fixed":["10.0.26100.2894"],"affected":"< 10.0.26100.2894","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","hyper-v","infrastructure","multi-user-hosts","windows","windows-server"],"not_affected_if":["fully-patched-systems","hyper-v-not-enabled"],"how_to_check":"Check the installed Windows build against Microsoft's January 2025 security update for CVE-2025-21335 (unknown exact build numbers in sources)\nRun Get-WindowsFeature or check Hyper-V role presence on hosts (unknown exact command in sources)","fix":"Install the Microsoft January 2025 Windows security update for CVE-2025-21335\nIf patching is not possible, follow Microsoft's mitigation guidance (unknown in sources)","status":"open","published_at":"2025-01-14T00:00:00+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:52:42+00:00","updated_at":"2026-10-23T22:29:05+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-23T20:52:42Z","model":"claude-haiku-5-5","output":{"fix":"Install the Microsoft January 2025 Windows security update for CVE-2025-21335\nIf patching is not possible, follow Microsoft's mitigation guidance (unknown in sources)","reach":"local","impact":"high","summary":"A use-after-free bug in the Windows Hyper-V NT Kernel Integration VSP lets a local user corrupt kernel memory. An attacker who already has a local account can gain SYSTEM privileges, and CISA reports it is being exploited in the wild.","category":"infrastructure","who_cares":["windows","hyper-v","windows-server","multi-user-hosts"],"confidence":0.6,"needs_auth":"yes","worst_case":"Local user gains SYSTEM privileges, full control of the Windows host","analyst_note":"Confirm exact patched Windows builds and the Hyper-V enablement requirement from Microsoft's CVE-2025-21335 advisory; sources only give the KEV entry.","how_to_check":"Check the installed Windows build against Microsoft's January 2025 security update for CVE-2025-21335 (unknown exact build numbers in sources)\nRun Get-WindowsFeature or check Hyper-V role presence on hosts (unknown exact command in sources)","needs_analyst":true,"not_affected_if":["hyper-v-not-enabled","fully-patched-systems"],"user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"high"},"cost_usd":0.000515,"input_tokens":2646,"output_tokens":500,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2025':14A,17A '-21335':15A,18A '10':23A,27A '11':31A,35A,39A '2022':44A '2025':49A '21h2':24A '22h2':28A,32A '23h2':36A,45A '24h2':40A 'account':93B 'action':135C 'allow':125C 'alreadi':89B 'appli':136C 'attack':87B,128C 'bug':68B 'cisa':99B,133C 'contain':117C 'corrupt':83B 'cve':13A,16A 'discontinu':142C 'elev':9A 'exploit':50B,104B 'free':67B,122C 'gain':95B,130C 'host':58B 'hyper':3A,52B,73B,111C 'hyper-v':2A,51B,72B,110C 'infrastructur':54B 'instruct':140C 'integr':7A,77B,115C 'kernel':6A,76B,84B,114C 'let':79B 'local':81B,92B,127C 'memori':85B 'microsoft':19A,21A,25A,29A,33A,37A,41A,46A,108C 'mitig':137C,148C 'multi':56B 'multi-user-host':55B 'nt':5A,75B,113C 'per':138C 'privileg':11A,97B,132C 'product':146C 'report':100B 'requir':134C 'server':43A,48A,62B 'system':96B,131C 'unavail':150C 'use':65B,120C,143C 'use-after-fre':64B,119C 'user':57B,82B 'v':4A,53B,74B,112C 'vendor':139C 'vsp':8A,78B,116C 'vulner':12A,123C 'wild':107B 'window':1A,59B,61B,71B,109C 'windows':20A,22A,26A,30A,34A,38A,42A,47A 'windows-serv':60B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2025-01-14T00:00:00+00:00","kev":{"dateAdded":"2025-01-14","dueDate":"2025-02-04","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-2025-21335","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2025-21335","severity":null,"published_at":"2025-01-14T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T10:39:05+00:00","note":null},{"source":"nvd","external_id":"CVE-2025-21335","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-21335","severity":null,"published_at":"2025-01-14T18:15:58+00:00","modified_at":"2026-09-24T13:10:00+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"}