{"id":"CVE-2026-31446","title":"ext4: fix use-after-free in update_super_work when racing with umount","summary":"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…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 < c8fe17a1b308c3d8c703ebfb049b325f844342c3","Linux >= b98535d091795a79336f520b0708457aacf55c67 < c4d829737329f2290dd41e290b7d75effdb2a7ff","Linux >= b98535d091795a79336f520b0708457aacf55c67 < 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d","Linux >= b98535d091795a79336f520b0708457aacf55c67 < 034053378dd81837fd6c7a43b37ee2e58d4f0b4e","Linux >= b98535d091795a79336f520b0708457aacf55c67 < c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe","Linux >= b98535d091795a79336f520b0708457aacf55c67 < 08b10e6f37fc533a759e9833af0692242e8b3f93","Linux >= b98535d091795a79336f520b0708457aacf55c67 < d15e4b0a418537aafa56b2cb80d44add83e83697","Linux 585ef03c9e79672781f954daae730dfe24bf3a46","Linux afe490e48d47df1b3f64012835c1bc2f075a8c8b","Linux >= 5.15.38 < 5.15.203","Linux >= 5.10.114 < 5.11","Linux >= 5.17.6 < 5.18","Linux 5.18"],"published":"2026-04-22","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:47:09.923Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31446","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"}],"tags":["cve.org"],"epss":0.00135,"epssPercentile":0.03336,"ingestedAt":"2026-09-08T15:33:26.990Z","slug":"CVE-2026-31446","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 < c8fe17a1b308c3d8c703ebfb049b325f844342c3`\n- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < c4d829737329f2290dd41e290b7d75effdb2a7ff`\n- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d`\n- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < 034053378dd81837fd6c7a43b37ee2e58d4f0b4e`\n- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe`\n- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < 08b10e6f37fc533a759e9833af0692242e8b3f93`\n- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < d15e4b0a418537aafa56b2cb80d44add83e83697`\n- `Linux 585ef03c9e79672781f954daae730dfe24bf3a46`\n- `Linux afe490e48d47df1b3f64012835c1bc2f075a8c8b`\n- `Linux >= 5.15.38 < 5.15.203`\n- `Linux >= 5.10.114 < 5.11`\n- `Linux >= 5.17.6 < 5.18`\n- `Linux 5.18`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}