{"id":"CVE-2026-98900","kind":"vulnerability","aliases":["CVE-2026-98900"],"related":[],"title":"Linux kernel: Xen grant allocation checks count too late, risking overflow","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nxen/gntalloc: validate grant count before allocation\n\ngntalloc_ioctl_alloc() allocates the grant-id array before checking\nwhether the requested count fits within the global grant limit. Counts\nabove that limit cannot succeed, so reject them before the\nuser-controlled allocation reaches kcalloc().\n\nUse a subtraction-based check while holding gref_mutex so adding the\nrequested count cannot wrap. Also cast the count before advancing the\nper-file index so the page-size multiplication is performed in 64-bit\narithmetic.","summary":"The Linux kernel's Xen grant-table allocator allocated a user-sized array before checking the count against the global limit, and the limit check could wrap. The fix rejects oversized counts earlier and does the page-size math in 64-bit, which blocks memory-exhaustion or overflow abuse from the ioctl path.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["infrastructure","linux-kernel","xen"],"not_affected_if":["no-gntalloc-device","no-xen"],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-23T12:18:24+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","triaged_at":"2026-10-25T04:59:55+00:00","updated_at":"2026-10-25T04:59:55+00:00","category":"infrastructure","confidence":0.5,"triage":{"at":"2026-10-25T04:59:55Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Linux kernel: Xen grant allocation checks count too late, risking overflow","impact":"medium","summary":"The Linux kernel's Xen grant-table allocator allocated a user-sized array before checking the count against the global limit, and the limit check could wrap. The fix rejects oversized counts earlier and does the page-size math in 64-bit, which blocks memory-exhaustion or overflow abuse from the ioctl path.","category":"infrastructure","nicknames":[],"who_cares":["linux-kernel","xen"],"confidence":0.5,"needs_auth":"unknown","worst_case":"local user may exhaust kernel memory or corrupt allocation state","analyst_note":"Find the fixed kernel stable versions and the CVSS score in the NVD entry at https://nvd.nist.gov/vuln/detail/CVE-2026-98900.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["no-xen","no-gntalloc-device"],"who_is_affected":"Only systems running Linux kernels that use the Xen gntalloc driver, typically Xen dom0 or hosts that expose /dev/xen/gntalloc. Systems without Xen or without that device node are not affected. The sources do not list fixed kernel versions.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000585,"input_tokens":3411,"output_tokens":487,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-98900':14A,17A '64':66B,171C 'abus':75B 'add':145C 'advanc':156C 'alloc':5A,31B,32B,95C,98C,99C,131C 'also':151C 'arithmet':173C 'array':37B,104C 'base':138C 'bit':67B,172C 'block':69B 'cannot':121C,149C 'cast':152C 'check':6A,39B,49B,106C,139C 'control':130C 'could':50B 'count':7A,41B,56B,93C,110C,117C,148C,154C 'cve':12A,15A 'earlier':57B 'exhaust':72B 'file':160C 'fit':111C 'fix':53B 'follow':85C 'global':44B,114C 'gntalloc':96C 'grant':4A,29B,92C,102C,115C 'grant-id':101C 'grant-tabl':28B 'gref':142C 'hold':141C 'id':103C 'index':161C 'infrastructur':18B 'ioctl':78B,97C 'kcalloc':133C 'kernel':2A,21B,25B,83C 'late':9A 'limit':45B,48B,116C,120C 'linux':1A,20B,24B,82C 'linux-kernel':19B 'math':64B 'memori':71B 'memory-exhaust':70B 'multipl':167C 'mutex':143C 'overflow':11A,74B 'overs':55B 'page':62B,165C 'page-s':61B,164C 'path':79B 'per':159C 'per-fil':158C 'perform':169C 'reach':132C 'reject':54B,124C 'request':109C,147C 'resolv':89C 'risk':10A 'size':36B,63B,166C 'subtract':137C 'subtraction-bas':136C 'succeed':122C 'tabl':30B 'use':134C 'user':35B,129C 'user-control':128C 'user-s':34B 'valid':91C 'vulner':86C 'whether':107C 'within':112C 'wrap':51B,150C 'xen':3A,22B,27B 'xen/gntalloc':90C","nicknames":[],"mitigations":[],"who_affected":"Only systems running Linux kernels that use the Xen gntalloc driver, typically Xen dom0 or hosts that expose /dev/xen/gntalloc. Systems without Xen or without that device node are not affected. The sources do not list fixed kernel versions.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T12:18:24+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98900","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98900","severity":null,"published_at":"2026-10-23T12:18:24+00:00","modified_at":"2026-10-23T12:18:24+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","fetched_at":"2026-10-23T22:29:03+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"}