{"id":"CVE-2026-99226","kind":"vulnerability","aliases":["CVE-2026-99226"],"related":[],"title":"Linux kernel: named keyring lookup can read freed memory during chown","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nkeys: Avoid the owner account dereference in named keyring lookup\n\nNamed keyring lookup must keep the storage containing the owner UID\nalive through the namespace mapping check.  find_keyring_by_name()\nreads keyring->user->uid under keyring_name_lock, but that lock protects\nthe keyring's name entry and allocation, not its separate key_user.\n\nA named session-keyring join can overlap a privileged KEYCTL_CHOWN on\nanother CPU.  If the keyring holds the last reference to its old dynamic\nkey_user and the ownership transfer succeeds, the following ordering is\npossible:\n\n    Named join                         Chown\n    find_keyring_by_name()              keyctl_chown_key()\n      read_lock(keyring_name_lock)       down_write(key->sem)\n      load old keyring->user\n                                         replace key->user and key->uid\n                                         up_write(key->sem)\n                                         key_put(key)\n                                         key_user_put(old user): free\n      read old user->uid\n      read_unlock(keyring_name_lock)\n\nChown neither takes keyring_name_lock nor key_session_mutex, so it can\nfree the old account between the pointer load and the UID read.  The\nlookup then reads freed memory even though the keyring itself is alive.\n\nUse keyring->uid for the mapping check.  key_alloc() initializes this\ninline owner UID and keyctl_chown_key() updates it on chown.\nThe existing name lock keeps its containing keyring allocated throughout\nthe check, so lookup no longer depends on the account's lifetime.  This\nalso matches the owner UID used by the permission check.\n\nKASAN report as below:\n\n    BUG: KASAN: slab-use-after-free in find_keyring_by_name+0x577/0x5d0\n    Read of size 4 at addr ffff8881128ae2ec by task keycase/500","summary":"A race in the Linux kernel's keyring code lets a named session-keyring join read an account structure that a privileged chown has already freed. The read is a use-after-free, which can crash the kernel or, if an attacker controls the freed memory, may allow further impact the sources do not describe.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["kernel","keyring","linux","multi-user-hosts","runtime"],"not_affected_if":["no-local-users","patched-kernel"],"how_to_check":"- Check the running kernel version with `uname -r` and compare it against the fixed kernel versions in the NVD entry.\n- Confirm whether the kernel is built with KASAN or is otherwise exposed to local users who can call keyctl joins.","fix":null,"status":"open","published_at":"2026-11-02T16:17:47+00:00","first_seen_at":"2026-11-02T16:24:05+00:00","triaged_at":"2026-11-02T16:26:57+00:00","updated_at":"2026-11-02T16:26:57+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-11-02T16:26:57Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Linux kernel: named keyring lookup can read freed memory during chown","impact":"high","summary":"A race in the Linux kernel's keyring code lets a named session-keyring join read an account structure that a privileged chown has already freed. The read is a use-after-free, which can crash the kernel or, if an attacker controls the freed memory, may allow further impact the sources do not describe.","audience":"businesses","category":"runtime","nicknames":[],"who_cares":["linux","kernel","keyring","multi-user-hosts"],"confidence":0.6,"fix_status":"unknown","needs_auth":"yes","worst_case":"local user reads freed kernel memory, possible crash or privilege escalation","analyst_note":"Find the affected kernel version ranges and fixed commit from the NVD entry at https://nvd.nist.gov/vuln/detail/CVE-2026-99226 and the upstream kernel stable tree.","how_to_check":"- Check the running kernel version with `uname -r` and compare it against the fixed kernel versions in the NVD entry.\n- Confirm whether the kernel is built with KASAN or is otherwise exposed to local users who can call keyctl joins.","plain_action":"","needs_analyst":true,"not_affected_if":["patched-kernel","no-local-users"],"who_is_affected":"Systems running affected Linux kernel builds where local users can create or join named keyrings. The sources describe a local race that needs a privileged chown on another CPU, so exposure depends on the kernel version and on who can run keyctl on the host. unknown whether the sources list a specific affected range.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000762,"input_tokens":4647,"output_tokens":595,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':346C '-2026':13A,16A '-99226':14A,17A '4':351C 'account':44B,97C,253C,316C 'addr':353C 'aliv':114C,274C 'alloc':142C,283C,305C 'allow':75B 'alreadi':51B 'also':320C 'anoth':161C 'attack':69B 'avoid':94C 'bug':334C 'check':119C,281C,308C,329C 'chown':11A,49B,159C,188C,194C,237C,291C,296C 'code':34B 'contain':110C,303C 'control':70B 'cpu':162C 'crash':63B 'cve':12A,15A 'depend':313C 'derefer':98C 'describ':82B 'dynam':173C 'entri':140C 'even':268C 'exist':298C 'ffff8881128ae2ec':354C 'find':120C,189C,342C 'follow':88C,182C 'free':60B,227C,250C,340C 'freed':8A,52B,72B,266C 'hold':166C 'host':24B 'impact':77B 'initi':284C 'inlin':286C 'join':41B,153C,187C 'kasan':330C,335C 'keep':107C,301C 'kernel':2A,18B,31B,65B,86C 'key':93C,146C,174C,195C,203C,210C,213C,217C,219C,221C,222C,244C,282C,292C 'keycase/500':357C 'keyctl':158C,193C,290C 'keyr':4A,19B,33B,40B,101C,104C,121C,125C,129C,137C,152C,165C,190C,198C,207C,234C,240C,271C,276C,304C,343C 'last':168C 'let':35B 'lifetim':318C 'linux':1A,20B,30B,85C 'load':205C,257C 'lock':131C,134C,197C,200C,236C,242C,300C 'longer':312C 'lookup':5A,102C,105C,263C,310C 'map':118C,280C 'match':321C 'may':74B 'memori':9A,73B,267C 'multi':22B 'multi-user-host':21B 'must':106C 'mutex':246C 'name':3A,37B,100C,103C,123C,130C,139C,149C,186C,192C,199C,235C,241C,299C,345C 'namespac':117C 'neither':238C 'old':172C,206C,225C,229C,252C 'order':183C 'overlap':155C 'owner':96C,112C,287C,323C 'ownership':178C 'permiss':328C 'pointer':256C 'possibl':185C 'privileg':48B,157C 'protect':135C 'put':220C,224C 'race':27B 'read':7A,42B,54B,124C,196C,228C,232C,261C,265C,348C 'refer':169C 'replac':209C 'report':331C 'resolv':92C 'runtim':25B 'sem':204C,218C 'separ':145C 'session':39B,151C,245C 'session-keyr':38B,150C 'size':350C 'slab':337C 'slab-use-after-fre':336C 'sourc':79B 'storag':109C 'structur':45B 'succeed':180C 'take':239C 'task':356C 'though':269C 'throughout':306C 'transfer':179C 'uid':113C,127C,214C,231C,260C,277C,288C,324C 'unlock':233C 'updat':293C 'use':58B,275C,325C,338C 'use-after-fre':57B 'user':23B,126C,147C,175C,208C,211C,223C,226C,230C 'vulner':89C 'write':202C,216C 'x577/0x5d0':347C","nicknames":[],"mitigations":[],"who_affected":"Systems running affected Linux kernel builds where local users can create or join named keyrings. The sources describe a local race that needs a privileged chown on another CPU, so exposure depends on the kernel version and on who can run keyctl on the host. unknown whether the sources list a specific affected range.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"unknown","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["kernel","keyring","linux","multiuserhosts","runtime","unknown"],"first_public_at":"2026-11-02T16:17:47+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99226","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99226","severity":null,"published_at":"2026-11-02T16:17:47+00:00","modified_at":"2026-11-02T16:17:47+00:00","first_seen_at":"2026-11-02T16:24:05+00:00","fetched_at":"2026-11-02T16:24:05+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"}