{"id":"CVE-2026-31446","state":"PUBLISHED","title":"ext4: fix use-after-free in update_super_work when racing with umount","description":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: fix use-after-free in update_super_work when racing with umount\n\nCommit b98535d09179 (\"ext4: fix bug_on in start_this_handle during umount\nfilesystem\") moved ext4_unregister_sysfs() before flushing s_sb_upd_work\nto prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups\nreads during unmount. However, this introduced a use-after-free because\nupdate_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which\naccesses the kobject's kernfs_node after it has been freed by kobject_del()\nin ext4_unregister_sysfs():\n\n  update_super_work                ext4_put_super\n  -----------------                --------------\n                                   ext4_unregister_sysfs(sb)\n                                     kobject_del(&sbi->s_kobj)\n                                       __kobject_del()\n                                         sysfs_remove_dir()\n                                           kobj->sd = NULL\n                                         sysfs_put(sd)\n                                           kernfs_put()  // RCU free\n  ext4_notify_error_sysfs(sbi)\n    sysfs_notify(&sbi->s_kobj)\n      kn = kobj->sd              // stale pointer\n      kernfs_get(kn)             // UAF on freed kernfs_node\n                                   ext4_journal_destroy()\n                                     flush_work(&sbi->s_sb_upd_work)\n\nInstead of reordering the teardown sequence, fix this by making\next4_notify_error_sysfs() detect that sysfs has already been torn down\nby checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call\nin that case. A dedicated mutex (s_error_notify_mutex) serializes\next4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()\nto prevent TOCTOU races where the kobject could be deleted between the\nstate_in_sysfs check and the sysfs_notify() call.","publishedAt":"2026-04-22T13:53:42.751Z","updatedAt":"2026-10-19T18:35:48.381Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"52c3a04f9ec2a16a4204d6274db338cb8d5b2d74","status":"affected","lessThan":"c8fe17a1b308c3d8c703ebfb049b325f844342c3","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"c4d829737329f2290dd41e290b7d75effdb2a7ff","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"9449f99ba04f5dd1c8423ad8a90b3651d7240d1d","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"034053378dd81837fd6c7a43b37ee2e58d4f0b4e","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"08b10e6f37fc533a759e9833af0692242e8b3f93","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"d15e4b0a418537aafa56b2cb80d44add83e83697","versionType":"git"},{"version":"585ef03c9e79672781f954daae730dfe24bf3a46","status":"affected","versionType":"git"},{"version":"afe490e48d47df1b3f64012835c1bc2f075a8c8b","status":"affected","versionType":"git"},{"version":"5.15.38","status":"affected","lessThan":"5.15.203","versionType":"semver"},{"version":"5.10.114","status":"affected","lessThan":"5.11","versionType":"semver"},{"version":"5.17.6","status":"affected","lessThan":"5.18","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/ext4.h","fs/ext4/super.c","fs/ext4/sysfs.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.18","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.168","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.131","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.80","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.21","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.11","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/ext4.h","fs/ext4/super.c","fs/ext4/sysfs.c"]}],"references":["https://git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3","https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff","https://git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d","https://git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e","https://git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe","https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93","https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31446.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31446","state":"PUBLISHED","datePublished":"2026-04-22T13:53:42.751Z","dateUpdated":"2026-10-19T18:35:48.381Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.091Z"},"containers":{"cna":{"title":"ext4: fix use-after-free in update_super_work when racing with umount","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: fix use-after-free in update_super_work when racing with umount\n\nCommit b98535d09179 (\"ext4: fix bug_on in start_this_handle during umount\nfilesystem\") moved ext4_unregister_sysfs() before flushing s_sb_upd_work\nto prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups\nreads during unmount. However, this introduced a use-after-free because\nupdate_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which\naccesses the kobject's kernfs_node after it has been freed by kobject_del()\nin ext4_unregister_sysfs():\n\n  update_super_work                ext4_put_super\n  -----------------                --------------\n                                   ext4_unregister_sysfs(sb)\n                                     kobject_del(&sbi->s_kobj)\n                                       __kobject_del()\n                                         sysfs_remove_dir()\n                                           kobj->sd = NULL\n                                         sysfs_put(sd)\n                                           kernfs_put()  // RCU free\n  ext4_notify_error_sysfs(sbi)\n    sysfs_notify(&sbi->s_kobj)\n      kn = kobj->sd              // stale pointer\n      kernfs_get(kn)             // UAF on freed kernfs_node\n                                   ext4_journal_destroy()\n                                     flush_work(&sbi->s_sb_upd_work)\n\nInstead of reordering the teardown sequence, fix this by making\next4_notify_error_sysfs() detect that sysfs has already been torn down\nby checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call\nin that case. A dedicated mutex (s_error_notify_mutex) serializes\next4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()\nto prevent TOCTOU races where the kobject could be deleted between the\nstate_in_sysfs check and the sysfs_notify() call."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"52c3a04f9ec2a16a4204d6274db338cb8d5b2d74","status":"affected","lessThan":"c8fe17a1b308c3d8c703ebfb049b325f844342c3","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"c4d829737329f2290dd41e290b7d75effdb2a7ff","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"9449f99ba04f5dd1c8423ad8a90b3651d7240d1d","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"034053378dd81837fd6c7a43b37ee2e58d4f0b4e","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"08b10e6f37fc533a759e9833af0692242e8b3f93","versionType":"git"},{"version":"b98535d091795a79336f520b0708457aacf55c67","status":"affected","lessThan":"d15e4b0a418537aafa56b2cb80d44add83e83697","versionType":"git"},{"version":"585ef03c9e79672781f954daae730dfe24bf3a46","status":"affected","versionType":"git"},{"version":"afe490e48d47df1b3f64012835c1bc2f075a8c8b","status":"affected","versionType":"git"},{"version":"5.15.38","status":"affected","lessThan":"5.15.203","versionType":"semver"},{"version":"5.10.114","status":"affected","lessThan":"5.11","versionType":"semver"},{"version":"5.17.6","status":"affected","lessThan":"5.18","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/ext4.h","fs/ext4/super.c","fs/ext4/sysfs.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.18","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.168","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.131","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.80","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.21","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.11","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/ext4.h","fs/ext4/super.c","fs/ext4/sysfs.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3"},{"url":"https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff"},{"url":"https://git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d"},{"url":"https://git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e"},{"url":"https://git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe"},{"url":"https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93"},{"url":"https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable ext4 paths are reached through local filesystem operations such as mounting/unmounting an ext4 image, reading ext4 procfs state, or writing ext4 sysfs controls; there is no direct network packet path.\nAC:L - The race is between queued ext4 superblock error work and teardown, and a crafted/ext4-error scenario can repeatedly drive the work while unmount/cleanup proceeds; under the required rule, this attacker-influenced race is Low complexity.\nPR:N - Directly initiating mount/umount or sysfs error injection requires CAP_SYS_ADMIN in the initial namespace, but a highest-severity reasonable scenario is an attacker-supplied crafted ext4 filesystem image mounted/unmounted by a victim or privileged automounter, requiring no attacker privilege.\nUI:R - Exploitation in the no-attacker-privilege scenario requires a victim or privileged system component to mount and later unmount/process the malicious ext4 filesystem image.\nS:U - The corruption occurs inside the kernel filesystem/sysfs/kernfs lifetime management for the same host kernel security authority; it is not a VM escape or cross-authority boundary break.\nC:H - The bug is a use-after-free of a kernfs_node reached through sysfs_notify after kobject deletion, and kernel UAFs are treated as capable of enabling high-impact information disclosure.\nI:H - The stale kernfs_node is refcounted and used after free, giving a memory-corruption primitive that is defensibly treated as potentially exploitable for kernel control-flow or data modification.\nA:H - At minimum the UAF can crash or oops the kernel during ext4 unmount/error-work processing, causing high availability 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