CVE-2026-31446 (GCVE-0-2026-31446)
Vulnerability from cvelistv5
Published
2026-04-22 13:53
Modified
2026-10-19 18:35
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ext4: fix use-after-free in update_super_work when racing with umount Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups reads during unmount. However, this introduced a use-after-free because update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which accesses the kobject's kernfs_node after it has been freed by kobject_del() in ext4_unregister_sysfs(): update_super_work ext4_put_super ----------------- -------------- ext4_unregister_sysfs(sb) kobject_del(&sbi->s_kobj) __kobject_del() sysfs_remove_dir() kobj->sd = NULL sysfs_put(sd) kernfs_put() // RCU free ext4_notify_error_sysfs(sbi) sysfs_notify(&sbi->s_kobj) kn = kobj->sd // stale pointer kernfs_get(kn) // UAF on freed kernfs_node ext4_journal_destroy() flush_work(&sbi->s_sb_upd_work) Instead of reordering the teardown sequence, fix this by making ext4_notify_error_sysfs() detect that sysfs has already been torn down by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call in that case. A dedicated mutex (s_error_notify_mutex) serializes ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs() to prevent TOCTOU races where the kobject could be deleted between the state_in_sysfs check and the sysfs_notify() call.
References
Impacted products
Vendor Product Version
Linux Linux Version: 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74
Version: b98535d091795a79336f520b0708457aacf55c67
Version: b98535d091795a79336f520b0708457aacf55c67
Version: b98535d091795a79336f520b0708457aacf55c67
Version: b98535d091795a79336f520b0708457aacf55c67
Version: b98535d091795a79336f520b0708457aacf55c67
Version: b98535d091795a79336f520b0708457aacf55c67
Version: 585ef03c9e79672781f954daae730dfe24bf3a46
Version: afe490e48d47df1b3f64012835c1bc2f075a8c8b
Version: 5.15.38   ≤
Version: 5.10.114   ≤
Version: 5.17.6   ≤
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    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-31446\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-10-16T15:09:20.883316Z\"}}}], \"providerMetadata\": {\"shortName\": \"CISA-ADP\", \"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"dateUpdated\": \"2026-10-16T15:09:21.465Z\"}}], \"cna\": {\"title\": \"ext4: fix use-after-free in update_super_work when racing with umount\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 7.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H\"}, \"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 impact.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"52c3a04f9ec2a16a4204d6274db338cb8d5b2d74\", \"lessThan\": \"c8fe17a1b308c3d8c703ebfb049b325f844342c3\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b98535d091795a79336f520b0708457aacf55c67\", \"lessThan\": \"c4d829737329f2290dd41e290b7d75effdb2a7ff\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b98535d091795a79336f520b0708457aacf55c67\", \"lessThan\": \"9449f99ba04f5dd1c8423ad8a90b3651d7240d1d\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b98535d091795a79336f520b0708457aacf55c67\", \"lessThan\": \"034053378dd81837fd6c7a43b37ee2e58d4f0b4e\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b98535d091795a79336f520b0708457aacf55c67\", \"lessThan\": \"c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b98535d091795a79336f520b0708457aacf55c67\", \"lessThan\": \"08b10e6f37fc533a759e9833af0692242e8b3f93\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b98535d091795a79336f520b0708457aacf55c67\", \"lessThan\": \"d15e4b0a418537aafa56b2cb80d44add83e83697\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"585ef03c9e79672781f954daae730dfe24bf3a46\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"afe490e48d47df1b3f64012835c1bc2f075a8c8b\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5.15.38\", \"lessThan\": \"5.15.203\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.10.114\", \"lessThan\": \"5.11\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.17.6\", \"lessThan\": \"5.18\", \"versionType\": \"semver\"}], \"programFiles\": [\"fs/ext4/ext4.h\", \"fs/ext4/super.c\", \"fs/ext4/sysfs.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.18\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.18\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.15.203\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.168\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.131\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.80\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.18.21\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.18.*\"}, {\"status\": \"unaffected\", \"version\": \"6.19.11\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.19.*\"}, {\"status\": \"unaffected\", \"version\": \"7.0\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"fs/ext4/ext4.h\", \"fs/ext4/super.c\", \"fs/ext4/sysfs.c\"], \"defaultStatus\": \"affected\"}], \"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\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"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() -\u003e sysfs_notify() which\\naccesses the kobject\u0027s 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(\u0026sbi-\u003es_kobj)\\n                                       __kobject_del()\\n                                         sysfs_remove_dir()\\n                                           kobj-\u003esd = NULL\\n                                         sysfs_put(sd)\\n                                           kernfs_put()  // RCU free\\n  ext4_notify_error_sysfs(sbi)\\n    sysfs_notify(\u0026sbi-\u003es_kobj)\\n      kn = kobj-\u003esd              // stale pointer\\n      kernfs_get(kn)             // UAF on freed kernfs_node\\n                                   ext4_journal_destroy()\\n                                     flush_work(\u0026sbi-\u003es_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.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.203\", \"versionStartIncluding\": \"5.15.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.168\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.131\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.80\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.18.21\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.19.11\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.0\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.10.114\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.17.6\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T12:22:36.689Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-31446\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-15T01:16:16.672Z\", \"dateReserved\": \"2026-03-09T15:48:24.091Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2026-04-22T13:53:42.751Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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