{"id":"CVE-2026-99175","kind":"vulnerability","aliases":["CVE-2026-99175"],"related":[],"title":"Linux kernel: fsnotify mark race lets an unprivileged fdinfo read crash","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfsnotify: prevent mark additions during connector teardown\n\nfsnotify_destroy_marks() keeps a reference to its current mark while it\ndrops conn->lock to destroy the mark. This stabilizes the forward-walk\ncursor, but does not prevent a new mark from being inserted before it.\nFor example, an inotify watch re-added after IN_IGNORED sorts before the\nold, detached mark for the same group. The walk can miss the replacement\nand then detach the entire connector from the object.\n\nThe replacement is still on its group's marks_list and, for inotify, in\nthe watch IDR. The group mutex no longer protects the connector's object\nfrom disappearing. An unprivileged fdinfo read racing the final detach\ncan consequently call igrab(NULL):\n\n  BUG: KASAN: null-ptr-deref in igrab+0x24/0x100\n  Write of size 4 at addr 0000000000000148\n  Call Trace:\n   igrab+0x24/0x100\n   inotify_show_fdinfo+0x1dc/0x5e0\n   seq_show+0x397/0x690\n\nSet a DESTROYING flag under conn->lock before starting the walk, and\nreject new marks on that connector with -ENOENT. The existing add-mark\nerror paths undo the temporary group-list entry and the backend's watch\nallocation. Do not wait for teardown while holding the group mutex,\nwhich the destroyer needs. Once the old connector is detached, an add\ncan install a fresh connector as before.\n\nThis closes the insertion race for all object types using the common\nconnector teardown, without changing the mark reference or SRCU lifetime\nrules.","summary":"A race in the kernel's fsnotify connector teardown can let a new mark be inserted during detach, so a concurrent unprivileged read of inotify fdinfo dereferences a NULL inode and triggers a KASAN null-pointer crash. The sources describe a kernel memory-safety bug with a crash on the read path; they do not say whether code execution is possible.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["linux-kernel","local-users","runtime","self-hosted"],"not_affected_if":["kernel-patched"],"how_to_check":"- Run `uname -r` and compare against the kernel versions listed in the NVD record for CVE-2026-99175 (unknown in the sources provided)\n- Check whether your distribution's kernel advisory lists this fix: unknown","fix":"- Update the Linux kernel to a release that includes the upstream commit 'fsnotify: prevent mark additions during connector teardown'; exact fixed versions: unknown\n- Reboot after installing the kernel package","status":"open","published_at":"2026-10-28T11:17:38+00:00","first_seen_at":"2026-10-28T11:32:36+00:00","triaged_at":"2026-10-28T11:35:31+00:00","updated_at":"2026-10-28T11:35:31+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-28T11:35:31Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the upstream commit 'fsnotify: prevent mark additions during connector teardown'; exact fixed versions: unknown\n- Reboot after installing the kernel package","reach":"local","title":"Linux kernel: fsnotify mark race lets an unprivileged fdinfo read crash","impact":"medium","summary":"A race in the kernel's fsnotify connector teardown can let a new mark be inserted during detach, so a concurrent unprivileged read of inotify fdinfo dereferences a NULL inode and triggers a KASAN null-pointer crash. The sources describe a kernel memory-safety bug with a crash on the read path; they do not say whether code execution is possible.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","self-hosted","local-users"],"confidence":0.5,"needs_auth":"yes","worst_case":"local user crashes kernel with null-pointer dereference during fdinfo read","analyst_note":"Find affected kernel version ranges and the stable backport commit IDs from the NVD entry or kernel.org stable mailing list; the sources give no versions.","how_to_check":"- Run `uname -r` and compare against the kernel versions listed in the NVD record for CVE-2026-99175 (unknown in the sources provided)\n- Check whether your distribution's kernel advisory lists this fix: unknown","needs_analyst":true,"not_affected_if":["kernel-patched"],"who_is_affected":"Systems running a Linux kernel without the fsnotify teardown fix, where unprivileged local users can read inotify fdinfo (/proc/<pid>/fdinfo) while watches are being removed. The sources do not say which kernel versions are affected or whether default distributions expose the path. Hosts that do not run untrusted local users have lower exposure.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000711,"input_tokens":3761,"output_tokens":669,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':232C,244C,249C,253C '-2026':13A,16A '-99175':14A,17A '0000000000000148':240C '4':237C 'add':153C,278C,316C 'add-mark':277C 'addit':104C 'addr':239C 'alloc':294C 'backend':291C 'bug':74B,224C 'call':221C,241C 'chang':339C 'close':325C 'code':87B 'common':335C 'concurr':48B 'conn':121C,260C 'connector':35B,106C,178C,206C,272C,312C,321C,336C 'consequ':220C 'crash':11A,65B,77B 'current':116C 'cursor':133C 'cve':12A,15A 'deref':229C 'derefer':54B 'describ':68B 'destroy':109C,124C,257C,307C 'detach':45B,161C,175C,218C,314C 'disappear':210C 'drop':120C 'enoent':274C 'entir':177C 'entri':288C 'error':280C 'exampl':147C 'execut':88B 'exist':276C 'fdinfo':9A,53B,213C,248C 'final':217C 'flag':258C 'follow':96C 'forward':131C 'forward-walk':130C 'fresh':320C 'fsnotifi':3A,34B,101C,108C 'group':166C,188C,200C,286C,303C 'group-list':285C 'hold':301C 'host':27B 'idr':198C 'ignor':156C 'igrab':222C,231C,243C 'inod':57B 'inotifi':52B,149C,194C,246C 'insert':43B,143C,327C 'instal':318C 'kasan':61B,225C 'keep':111C 'kernel':2A,20B,32B,70B,94C 'let':6A,38B 'lifetim':345C 'linux':1A,19B,93C 'linux-kernel':18B 'list':191C,287C 'local':22B 'local-us':21B 'lock':122C,261C 'longer':203C 'mark':4A,41B,103C,110C,117C,126C,140C,162C,190C,269C,279C,341C 'memori':72B 'memory-safeti':71B 'miss':170C 'mutex':201C,304C 'need':308C 'new':40B,139C,268C 'null':56B,63B,223C,227C 'null-point':62B 'null-ptr-deref':226C 'object':181C,208C,331C 'old':160C,311C 'path':81B,281C 'pointer':64B 'possibl':90B 'prevent':102C,137C 'protect':204C 'ptr':228C 'race':5A,29B,215C,328C 're':152C 're-ad':151C 'read':10A,50B,80B,214C 'refer':113C,342C 'reject':267C 'replac':172C,183C 'resolv':100C 'rule':346C 'runtim':24B 'safeti':73B 'say':85B 'self':26B 'self-host':25B 'seq':251C 'set':255C 'show':247C,252C 'size':236C 'sort':157C 'sourc':67B 'srcu':344C 'stabil':128C 'start':263C 'still':185C 'teardown':36B,107C,299C,337C 'temporari':284C 'trace':242C 'trigger':59B 'type':332C 'undo':282C 'unprivileg':8A,49B,212C 'use':333C 'user':23B 'vulner':97C 'wait':297C 'walk':132C,168C,265C 'watch':150C,197C,293C 'whether':86B 'without':338C 'write':234C 'x1dc/0x5e0':250C 'x24/0x100':233C,245C 'x397/0x690':254C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel without the fsnotify teardown fix, where unprivileged local users can read inotify fdinfo (/proc/<pid>/fdinfo) while watches are being removed. The sources do not say which kernel versions are affected or whether default distributions expose the path. Hosts that do not run untrusted local users have lower exposure.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T11:17:38+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99175","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99175","severity":null,"published_at":"2026-10-28T11:17:38+00:00","modified_at":"2026-10-28T11:17:38+00:00","first_seen_at":"2026-10-28T11:32:36+00:00","fetched_at":"2026-10-28T11:32:36+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"}