{"id":"CVE-2026-98788","kind":"vulnerability","aliases":["CVE-2026-98788"],"related":[],"title":"Linux kernel: futex private hash resize can free memory still in use","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Fix private hash use-after-free on resize\n\npoll_state_synchronize_rcu(mm->futex.phash.batches) is used by\nfutex_ref_drop() to check that a grace period has passed since the\ncurrent hash was published. This relies on batches referencing a grace\nperiod which started after the hash pointer was assigned.\n\n__futex_pivot_hash() sets mmph->batches before it replaces mmph->hash:\n\n    scoped_guard(rcu) {\n            mmph->batches = get_state_synchronize_rcu();\n            rcu_assign_pointer(mmph->hash, new);\n    }\n\nThe scoped_guard(rcu) doesn't stop new grace periods from starting, and\nif one starts between those two assignments, futex_ref_drop() can move\nforward while a reader still holds a pointer to the old hash.\n\nFix things by setting mmph->batches after assigning mmph->hash.  The\nscoped_guard(rcu) isn't needed, so let's drop that as well.","summary":"When the kernel resizes a process's private futex hash table, a race can let the old table be freed while a reader still holds a pointer to it. The sources do not say what an attacker can do with the freed memory beyond the use-after-free itself.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["futex","linux-kernel","runtime"],"not_affected_if":[],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-18T16:17:32+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:15:15+00:00","updated_at":"2026-10-25T05:15:15+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T05:15:15Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Linux kernel: futex private hash resize can free memory still in use","impact":"high","summary":"When the kernel resizes a process's private futex hash table, a race can let the old table be freed while a reader still holds a pointer to it. The sources do not say what an attacker can do with the freed memory beyond the use-after-free itself.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","futex"],"confidence":0.5,"needs_auth":"unknown","worst_case":"unknown; a use-after-free in the kernel, impact not stated","analyst_note":"Check the NVD entry and the upstream kernel commit for the fixed kernel versions and whether a local unprivileged user can trigger the race.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":[],"who_is_affected":"unknown","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000526,"input_tokens":3558,"output_tokens":341,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':14A,17A '-98788':15A,18A 'assign':134C,156C,180C,205C 'attack':60B 'batch':122C,140C,150C,203C 'beyond':67B 'check':106C 'current':115C 'cve':13A,16A 'doesn':165C 'drop':104C,183C,218C 'fix':84C,198C 'follow':78C 'forward':186C 'free':8A,72B,90C 'freed':43B,65B 'futex':3A,19B,32B,83C,102C,135C,181C 'futex.phash.batches':98C 'get':151C 'grace':109C,125C,169C 'guard':147C,163C,210C 'hash':5A,33B,86C,116C,131C,137C,145C,159C,197C,207C 'hold':48B,191C 'isn':212C 'kernel':2A,22B,26B,76C 'let':38B,216C 'linux':1A,21B,75C 'linux-kernel':20B 'memori':9A,66B 'mm':97C 'mmph':139C,144C,149C,158C,202C,206C 'move':185C 'need':214C 'new':160C,168C 'old':40B,196C 'one':175C 'pass':112C 'period':110C,126C,170C 'pivot':136C 'pointer':50B,132C,157C,193C 'poll':93C 'privat':4A,31B,85C 'process':29B 'publish':118C 'race':36B 'rcu':96C,148C,154C,155C,164C,211C 'reader':46B,189C 'ref':103C,182C 'referenc':123C 'reli':120C 'replac':143C 'resiz':6A,27B,92C 'resolv':82C 'runtim':23B 'say':57B 'scope':146C,162C,209C 'set':138C,201C 'sinc':113C 'sourc':54B 'start':128C,172C,176C 'state':94C,152C 'still':10A,47B,190C 'stop':167C 'synchron':95C,153C 'tabl':34B,41B 'thing':199C 'two':179C 'use':12A,70B,88C,100C 'use-after-fre':69B,87C 'vulner':79C 'well':221C","nicknames":[],"mitigations":[],"who_affected":null,"tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:32+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98788","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98788","severity":null,"published_at":"2026-10-18T16:17:32+00:00","modified_at":"2026-10-19T10:19:42+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","fetched_at":"2026-10-23T22:28:56+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"}