{"id":"CVE-2026-98991","state":"PUBLISHED","title":"namespace: queue a mount only once for mount notifications","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: queue a mount only once for mount notifications\n\nmnt_notify_add() puts a mount on notify_list. It doesn't check whether\nthe mount is on the list already. That's fine as long as every mount is\nqueued at most once per namespace_sem hold. It isn't.\n\npropagate_umount() moves a surviving overmount off a stack of mounts\nthat are going away and queues it as moved. shrink_submounts() and\nmark_mounts_for_expiry() call umount_tree() for several mounts under a\nsingle namespace_sem hold. So the second umount_tree() can take down\nexactly the mount the first one reparented, reparent it once more and so\nend up queueing it a second time.\n\nThe second list_add_tail() cuts the mounts queued in between out of the\nlist while the head still points at the last of them. notify_mnt_list()\nthen only visits that one mount and the others are freed after the grace\nperiod with notify_list still pointing at them. Every later mount\noperation on the host walks freed memory:\n\n  BUG: KASAN: slab-use-after-free in __list_add_valid_or_report\n  Read of size 8 at addr ffff8881003d57e0 by task notify_dq/162\n   __list_add_valid_or_report+0x15c/0x1a0\n   mnt_add_to_ns+0x322/0x890\n   attach_recursive_mnt.isra.0+0xf2a/0x1a00\n   path_mount+0x139c/0x1d40\n\nThis needs a mount with MNT_SHRINKABLE to bind from. That's what\nfinish_automount() creates (submounts of NFS, AFS and CIFS and the\ntracefs mount below debugfs). Bind mounts inherit the flag. A mount\nnamespace with a FAN_MARK_MNTNS mark does the rest and root in a user\nnamespace can have both.\n\nInitialize to_notify in alloc_vfsmnt() and leave a mount alone that is\nqueued already. mnt_notify() looks at the state the mount has when the\nlist is drained so a single entry per mount is enough. The move event\nfor a mount that is unmounted under the same hold is lost. That's fine.\nThe detach is what matters.","publishedAt":"2026-10-23T12:20:10.289Z","updatedAt":"2026-10-24T14:09:52.901Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"bf630c40164162ba1d3933c2f5e3397d083e0948","status":"affected","lessThan":"acbe9e4418e2ef7bef1a12e62e0e7d6145a15190","versionType":"git"},{"version":"bf630c40164162ba1d3933c2f5e3397d083e0948","status":"affected","lessThan":"702ff3fe499876e09c45558a05366d21a5bc41ab","versionType":"git"},{"version":"bf630c40164162ba1d3933c2f5e3397d083e0948","status":"affected","lessThan":"bd2feb7796b6585938a4241e7b7c4148a6f7b762","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/mount.h","fs/namespace.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.15","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/mount.h","fs/namespace.c"]}],"references":["https://git.kernel.org/stable/c/acbe9e4418e2ef7bef1a12e62e0e7d6145a15190","https://git.kernel.org/stable/c/702ff3fe499876e09c45558a05366d21a5bc41ab","https://git.kernel.org/stable/c/bd2feb7796b6585938a4241e7b7c4148a6f7b762"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98991.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98991","state":"PUBLISHED","datePublished":"2026-10-23T12:20:10.289Z","dateUpdated":"2026-10-24T14:09:52.901Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.384Z"},"containers":{"cna":{"title":"namespace: queue a mount only once for mount notifications","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: queue a mount only once for mount notifications\n\nmnt_notify_add() puts a mount on notify_list. It doesn't check whether\nthe mount is on the list already. That's fine as long as every mount is\nqueued at most once per namespace_sem hold. It isn't.\n\npropagate_umount() moves a surviving overmount off a stack of mounts\nthat are going away and queues it as moved. shrink_submounts() and\nmark_mounts_for_expiry() call umount_tree() for several mounts under a\nsingle namespace_sem hold. So the second umount_tree() can take down\nexactly the mount the first one reparented, reparent it once more and so\nend up queueing it a second time.\n\nThe second list_add_tail() cuts the mounts queued in between out of the\nlist while the head still points at the last of them. notify_mnt_list()\nthen only visits that one mount and the others are freed after the grace\nperiod with notify_list still pointing at them. Every later mount\noperation on the host walks freed memory:\n\n  BUG: KASAN: slab-use-after-free in __list_add_valid_or_report\n  Read of size 8 at addr ffff8881003d57e0 by task notify_dq/162\n   __list_add_valid_or_report+0x15c/0x1a0\n   mnt_add_to_ns+0x322/0x890\n   attach_recursive_mnt.isra.0+0xf2a/0x1a00\n   path_mount+0x139c/0x1d40\n\nThis needs a mount with MNT_SHRINKABLE to bind from. That's what\nfinish_automount() creates (submounts of NFS, AFS and CIFS and the\ntracefs mount below debugfs). Bind mounts inherit the flag. A mount\nnamespace with a FAN_MARK_MNTNS mark does the rest and root in a user\nnamespace can have both.\n\nInitialize to_notify in alloc_vfsmnt() and leave a mount alone that is\nqueued already. mnt_notify() looks at the state the mount has when the\nlist is drained so a single entry per mount is enough. The move event\nfor a mount that is unmounted under the same hold is lost. That's fine.\nThe detach is what matters."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"bf630c40164162ba1d3933c2f5e3397d083e0948","status":"affected","lessThan":"acbe9e4418e2ef7bef1a12e62e0e7d6145a15190","versionType":"git"},{"version":"bf630c40164162ba1d3933c2f5e3397d083e0948","status":"affected","lessThan":"702ff3fe499876e09c45558a05366d21a5bc41ab","versionType":"git"},{"version":"bf630c40164162ba1d3933c2f5e3397d083e0948","status":"affected","lessThan":"bd2feb7796b6585938a4241e7b7c4148a6f7b762","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/mount.h","fs/namespace.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.15","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/mount.h","fs/namespace.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/acbe9e4418e2ef7bef1a12e62e0e7d6145a15190"},{"url":"https://git.kernel.org/stable/c/702ff3fe499876e09c45558a05366d21a5bc41ab"},{"url":"https://git.kernel.org/stable/c/bd2feb7796b6585938a4241e7b7c4148a6f7b762"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - Local umount(2) follows ksys_umount()->path_umount()->do_umount()->shrink_submounts()->umount_tree()->propagate_umount()->reparent()->mnt_notify_add(), the function patched; no network protocol supplies the triggering mount topology.\nAC:L - With a reachable MNT_SHRINKABLE automount, the attacker can create the required bind, shared/slave, and overmount topology and synchronously unmount it; duplicate queueing occurs sequentially under one namespace_sem hold and requires no race.\nPR:L - may_mount() and FAN_MARK_MNTNS use CAP_SYS_ADMIN relative to the attacker-owned mount/group/target user namespaces; unshare(CLONE_NEWUSER|CLONE_NEWNS) gives an ordinary local user those namespace-scoped capabilities without init-namespace privilege.\nUI:N - The attacker personally creates the fanotify mark and mount topology and invokes umount(2); no victim must mount media, open a file, or perform another action.\nS:U - The corrupted global notify_list and freed struct mount objects are resources of the same host kernel reached by the attacker; this is a kernel privilege-escalation boundary, not a guest-host, IOMMU, or other scope change.\nC:H - notify_mnt_list() leaves notify_list linked through freed struct mount::to_notify nodes, so later mount operations dereference attacker-reclaimable mnt_cache objects; this kernel-heap UAF can be leveraged to disclose kernel memory.\nI:H - After the stale to_notify node is freed or reallocated, __list_add() in mnt_notify_add() writes next->prev and prev->next through the corrupted list links, providing exploitable kernel-heap corruption capable of control-flow hijacking.\nA:H - namespace_unlock() frees mounts still referenced by notify_list, and a later path_mount()->mnt_add_to_ns()->mnt_notify_add() provably reads the freed node, producing the documented KASAN slab-use-after-free and a host kernel oops or panic."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-24T14:09:52.901Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.2.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}