{"id":"CVE-2026-98985","kind":"vulnerability","aliases":["CVE-2026-98985"],"related":[],"title":"Linux kernel: pivot_root reads a freed mount parent, crashing or corrupting memory","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: check the mounts before reading their parents in pivot_root()\n\npath_pivot_root() reads the parents of new_root and of the caller's root\nand checks whether they are shared before it checks that either mount is\nin the caller's mount namespace. Only namespace_sem is held. That's fine\nfor a mount that is in the caller's mount namespace.\n\nBut new_root can be a file descriptor to a mount that has been unmounted\nand that only the file descriptor keeps alive. If that mount stayed\nattached to its parent when it was unmounted nothing pins the parent for\nit. The final mntput() of the parent unhooks the children under\nmount_lock alone and frees the parent afterwards:\n\n  pivot_root()                     close(fd), last ref on the parent\n  ------------                     ---------------------------------\n  ex_parent = new_mnt->mnt_parent\n                                   mntput_no_expire_slowpath()\n                                     __umount_mnt(new_mnt)\n                                   cleanup_mnt()\n                                     call_rcu()\n  IS_MNT_SHARED(ex_parent)\n\n  BUG: KASAN: slab-use-after-free in path_pivot_root+0xf1a/0x1840\n  Read of size 4 at addr ffff8881047382f8 by task pivot_widen/157\n   path_pivot_root+0xf1a/0x1840\n   __x64_sys_pivot_root+0x165/0x190\n\nThe same goes for the caller's root via chroot(). Both outcomes of the\ncheck end in EINVAL so nothing but the read itself goes wrong. It's the\nsame thing commit bb4609405752 (\"statmount: read the parent of an\nunmounted mount under mount_lock\") fixed for statmount().\n\nCheck that both mounts are in the caller's namespace before their\nparents are read. Every path returns EINVAL either way.","summary":"In the Linux kernel's pivot_root() and chroot() path, the kernel reads the parent of a mount that may already be freed after its last reference was dropped via a file descriptor. The sources describe a KASAN use-after-free read; the reported impact is a crash or memory corruption in kernel context, and the sources do not state a confirmed privilege escalation.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["containers","linux-kernel","runtime","self-hosted"],"not_affected_if":[],"how_to_check":"- unknown","fix":"- Update to a Linux kernel release that includes the upstream fix \"namespace: check the mounts before reading their parents in pivot_root()\" (the version is unknown from the sources)","status":"open","published_at":"2026-10-23T13:17:20+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","triaged_at":"2026-10-25T04:56:12+00:00","updated_at":"2026-10-25T04:56:12+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T04:56:12Z","model":"claude-haiku-5-5","output":{"fix":"- Update to a Linux kernel release that includes the upstream fix \"namespace: check the mounts before reading their parents in pivot_root()\" (the version is unknown from the sources)","reach":"local","title":"Linux kernel: pivot_root reads a freed mount parent, crashing or corrupting memory","impact":"high","summary":"In the Linux kernel's pivot_root() and chroot() path, the kernel reads the parent of a mount that may already be freed after its last reference was dropped via a file descriptor. The sources describe a KASAN use-after-free read; the reported impact is a crash or memory corruption in kernel context, and the sources do not state a confirmed privilege escalation.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","self-hosted","containers"],"confidence":0.5,"needs_auth":"unknown","worst_case":"kernel memory use-after-free read could crash the system or corrupt memory","analyst_note":"Find the affected kernel version range and the fixed stable release from the upstream kernel commit referenced in the NVD entry (https://nvd.nist.gov/vuln/detail/CVE-2026-98985); confirm whether unprivileged users can reach pivot_root or chroot in a user namespace.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":[],"who_is_affected":"Systems running a Linux kernel without the upstream fix for pivot_root() and chroot() mount parent checks. The sources do not say which kernel versions are affected or which configurations, so the exact scope is unknown.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000672,"input_tokens":3835,"output_tokens":577,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':269C,285C,291C '-2026':15A,18A '-98985':16A,19A '4':274C 'addr':276C 'afterward':225C 'aliv':189C 'alon':220C 'alreadi':48B 'attach':194C 'bb4609405752':325C 'bug':258C 'call':251C 'caller':126C,144C,163C,298C,347C 'check':104C,130C,137C,307C,340C 'children':216C 'chroot':36B,302C 'cleanup':249C 'close':228C 'commit':324C 'confirm':90B 'contain':20B 'context':82B 'corrupt':12A,79B 'crash':10A,76B 'cve':14A,17A 'describ':63B 'descriptor':60B,174C,187C 'drop':56B 'einval':310C,358C 'either':139C,359C 'end':308C 'escal':92B 'everi':355C 'ex':235C,256C 'expir':243C 'fd':229C 'ffff8881047382f8':277C 'file':59B,173C,186C 'final':209C 'fine':155C 'fix':337C 'follow':98C 'free':69B,222C,264C 'freed':7A,50B 'goe':295C,317C 'held':152C 'host':27B 'impact':73B 'kasan':65B,259C 'keep':188C 'kernel':2A,23B,31B,39B,81B,96C 'last':53B,230C 'linux':1A,22B,30B,95C 'linux-kernel':21B 'lock':219C,336C 'may':47B 'memori':13A,78B 'mnt':238C,239C,246C,248C,250C,254C 'mntput':210C,241C 'mount':8A,45B,106C,140C,146C,158C,165C,177C,192C,218C,333C,335C,343C 'namespac':103C,147C,149C,166C,349C 'new':121C,168C,237C,247C 'noth':202C,312C 'outcom':304C 'parent':9A,42B,110C,119C,197C,205C,213C,224C,234C,236C,240C,257C,329C,352C 'path':37B,114C,266C,282C,356C 'pin':203C 'pivot':3A,33B,112C,115C,226C,267C,280C,283C,289C 'privileg':91B 'rcu':252C 'read':5A,40B,70B,108C,117C,271C,315C,327C,354C 'ref':231C 'refer':54B 'report':72B 'resolv':102C 'return':357C 'root':4A,34B,113C,116C,122C,128C,169C,227C,268C,284C,290C,300C 'runtim':24B 'self':26B 'self-host':25B 'sem':150C 'share':134C,255C 'size':273C 'slab':261C 'slab-use-after-fre':260C 'slowpath':244C 'sourc':62B,85B 'state':88B 'statmount':326C,339C 'stay':193C 'sys':288C 'task':279C 'thing':323C 'umount':245C 'unhook':214C 'unmount':181C,201C,332C 'use':67B,262C 'use-after-fre':66B 'via':57B,301C 'vulner':99C 'way':360C 'whether':131C 'widen/157':281C 'wrong':318C 'x165/0x190':292C 'x64':287C 'xf1a/0x1840':270C,286C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel without the upstream fix for pivot_root() and chroot() mount parent checks. The sources do not say which kernel versions are affected or which configurations, so the exact scope is unknown.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T13:17:20+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98985","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98985","severity":null,"published_at":"2026-10-23T13:17:20+00:00","modified_at":"2026-10-23T13:17:20+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"}