Vulnerability-Lookup

GHSA-H4Q9-QCG7-RJ48

Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-24 15:32

Details

In the Linux kernel, the following vulnerability has been resolved:

namespace: reset the old parent's ->overmount in mnt_change_mountpoint()

__umount_mnt() resets ->overmount of the parent when it unmounts the mount that overmounts it. mnt_change_mountpoint() doesn't. It moves the mount to its new parent and leaves the old one pointing at it.

For a mount that is moved beneath in attach_recursive_mnt() that doesn't matter. The new mount has already reset ->overmount of the old parent by the time the old top mount is moved onto it.

It matters for reparent() though. propagate_umount() moves a surviving overmount onto the first ancestor that isn't going to be unmounted. The mount it was taken from is unmounted immediately afterwards. If a file descriptor keeps that unmounted mount alive ->overmount points at the moved mount. That's a dangling pointer and UAF as the moved mount is unmounted and freed.

do_lock_mount() follows ->overmount from the target path under mount_lock. With a file descriptor on such a mount as the target of a mount beneath topmost_overmount() walks into the freed mount and do_lock_mount() takes references on whatever it finds there.

So reset ->overmount of the old parent in mnt_change_mountpoint() the same way __umount_mnt() does. A mount's ->overmount is then always a mount that is attached to it.

Severity

7.8 (High)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98995"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-23T13:17:21Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: reset the old parent\u0027s -\u003eovermount in mnt_change_mountpoint()\n\n__umount_mnt() resets -\u003eovermount of the parent when it unmounts the\nmount that overmounts it. mnt_change_mountpoint() doesn\u0027t. It moves the\nmount to its new parent and leaves the old one pointing at it.\n\nFor a mount that is moved beneath in attach_recursive_mnt() that doesn\u0027t\nmatter. The new mount has already reset -\u003eovermount of the old parent by\nthe time the old top mount is moved onto it.\n\nIt matters for reparent() though. propagate_umount() moves a surviving\novermount onto the first ancestor that isn\u0027t going to be unmounted. The\nmount it was taken from is unmounted immediately afterwards. If a file\ndescriptor keeps that unmounted mount alive -\u003eovermount points at the\nmoved mount. That\u0027s a dangling pointer and UAF as the moved mount is\nunmounted and freed.\n\ndo_lock_mount() follows -\u003eovermount from the target path under\nmount_lock. With a file descriptor on such a mount as the target of a\nmount beneath topmost_overmount() walks into the freed mount and\ndo_lock_mount() takes references on whatever it finds there.\n\nSo reset -\u003eovermount of the old parent in mnt_change_mountpoint() the\nsame way __umount_mnt() does. A mount\u0027s -\u003eovermount is then always a\nmount that is attached to it.",
  "id": "GHSA-h4q9-qcg7-rj48",
  "modified": "2026-10-24T15:32:49Z",
  "published": "2026-10-23T15:31:34Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98995"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/08d575ee89393fd812dbdca7b5d7b4574cd5a564"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/476ef286a7a5db8bda51325dc0c45887b4d99d9a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5e0a1f2c753a79749bc2ead3ae2f2ede3941daa5"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-98995 (GCVE-0-2026-98995)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:20 – Updated: 2026-10-24 14:09

Title

namespace: reset the old parent's ->overmount in mnt_change_mountpoint()

Summary

In the Linux kernel, the following vulnerability has been resolved: namespace: reset the old parent's ->overmount in mnt_change_mountpoint() __umount_mnt() resets ->overmount of the parent when it unmounts the mount that overmounts it. mnt_change_mountpoint() doesn't. It moves the mount to its new parent and leaves the old one pointing at it. For a mount that is moved beneath in attach_recursive_mnt() that doesn't matter. The new mount has already reset ->overmount of the old parent by the time the old top mount is moved onto it. It matters for reparent() though. propagate_umount() moves a surviving overmount onto the first ancestor that isn't going to be unmounted. The mount it was taken from is unmounted immediately afterwards. If a file descriptor keeps that unmounted mount alive ->overmount points at the moved mount. That's a dangling pointer and UAF as the moved mount is unmounted and freed. do_lock_mount() follows ->overmount from the target path under mount_lock. With a file descriptor on such a mount as the target of a mount beneath topmost_overmount() walks into the freed mount and do_lock_mount() takes references on whatever it finds there. So reset ->overmount of the old parent in mnt_change_mountpoint() the same way __umount_mnt() does. A mount's ->overmount is then always a mount that is attached to it.

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 7056 records in the last 180 days details

References

3 references

URL	Tags
https://git.kernel.org/stable/c/5e0a1f2c753a79749…
https://git.kernel.org/stable/c/08d575ee89393fd81…
https://git.kernel.org/stable/c/476ef286a7a5db8bd…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: ffdc52fbbd5835a936ad683c943d6d103a2d4514 , < 5e0a1f2c753a79749bc2ead3ae2f2ede3941daa5 (git) Affected: ffdc52fbbd5835a936ad683c943d6d103a2d4514 , < 08d575ee89393fd812dbdca7b5d7b4574cd5a564 (git) Affected: ffdc52fbbd5835a936ad683c943d6d103a2d4514 , < 476ef286a7a5db8bda51325dc0c45887b4d99d9a (git)
Linux	Linux	Affected: 6.17 Unaffected: 0 , < 6.17 (semver) Unaffected: 6.18.57 , ≤ 6.18.* (semver) Unaffected: 7.2.11 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/namespace.c"
          ],
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              "status": "affected",
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              "versionType": "git"
            },
            {
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              "status": "affected",
              "version": "ffdc52fbbd5835a936ad683c943d6d103a2d4514",
              "versionType": "git"
            },
            {
              "lessThan": "476ef286a7a5db8bda51325dc0c45887b4d99d9a",
              "status": "affected",
              "version": "ffdc52fbbd5835a936ad683c943d6d103a2d4514",
              "versionType": "git"
            }
          ]
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          "versions": [
            {
              "status": "affected",
              "version": "6.17"
            },
            {
              "lessThan": "6.17",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.57",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.57",
                  "versionStartIncluding": "6.17",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.11",
                  "versionStartIncluding": "6.17",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "6.17",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: reset the old parent\u0027s -\u003eovermount in mnt_change_mountpoint()\n\n__umount_mnt() resets -\u003eovermount of the parent when it unmounts the\nmount that overmounts it. mnt_change_mountpoint() doesn\u0027t. It moves the\nmount to its new parent and leaves the old one pointing at it.\n\nFor a mount that is moved beneath in attach_recursive_mnt() that doesn\u0027t\nmatter. The new mount has already reset -\u003eovermount of the old parent by\nthe time the old top mount is moved onto it.\n\nIt matters for reparent() though. propagate_umount() moves a surviving\novermount onto the first ancestor that isn\u0027t going to be unmounted. The\nmount it was taken from is unmounted immediately afterwards. If a file\ndescriptor keeps that unmounted mount alive -\u003eovermount points at the\nmoved mount. That\u0027s a dangling pointer and UAF as the moved mount is\nunmounted and freed.\n\ndo_lock_mount() follows -\u003eovermount from the target path under\nmount_lock. With a file descriptor on such a mount as the target of a\nmount beneath topmost_overmount() walks into the freed mount and\ndo_lock_mount() takes references on whatever it finds there.\n\nSo reset -\u003eovermount of the old parent in mnt_change_mountpoint() the\nsame way __umount_mnt() does. A mount\u0027s -\u003eovermount is then always a\nmount that is attached to it."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Local umount2() reaches do_umount()-\u003eumount_tree()-\u003epropagate_umount()-\u003ereparent()-\u003emnt_change_mountpoint(), and local move_mount(MOVE_MOUNT_BENEATH) later consumes the dangling overmount; no network or physical input reaches this path.\nAC:L - The regression test deterministically creates the propagation topology, pins X_b, frees its reparented overmount, and triggers the UAF; no race or external state is required, and any mount-cache grooming is attacker-controlled.\nPR:L - can_umount() and move_mount() require may_mount(), but the test\u0027s unshare(CLONE_NEWUSER|CLONE_NEWNS) gives an ordinary local user CAP_SYS_ADMIN in the child mount namespace, satisfying every mount-operation gate without init-namespace root.\nUI:N - The attacker personally creates the shared/private tmpfs mounts, opens the O_PATH descriptor, performs both lazy unmounts, and invokes move_mount(); no victim must mount, open, or otherwise act on anything.\nS:U - The dangling struct mount created by mnt_change_mountpoint() corrupts the same host kernel that enforces the attacker\u0027s mount namespace; this is ordinary kernel privilege escalation, not a VM, hypervisor, or IOMMU boundary crossing.\nC:H - topmost_overmount() reads freed struct mount contents, and where_to_mount() then consumes its stale overmount, mnt_mountpoint, and mnt_parent pointers; reclaiming the mnt_cache object permits redirected kernel-memory accesses and high-impact disclosure.\nI:H - do_lock_mount() calls mntget() and dget() through the freed mount-derived pointers, causing reference-count writes through stale mnt_pcp and dentry state; mount-cache reclamation and heap grooming can turn these UAF writes into control-flow corruption.\nA:H - Following the freed overmount and then dereferencing or locking the stale dentry-\u003ed_inode can produce a kernel UAF oops or panic, and the complete mount/unmount/move_mount sequence is repeatable by the same unprivileged process."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:09:55.095Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/08d575ee89393fd812dbdca7b5d7b4574cd5a564"
        },
        {
          "url": "https://git.kernel.org/stable/c/476ef286a7a5db8bda51325dc0c45887b4d99d9a"
        }
      ],
      "title": "namespace: reset the old parent\u0027s -\u003eovermount in mnt_change_mountpoint()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98995",
    "datePublished": "2026-10-23T12:20:14.155Z",
    "dateReserved": "2026-09-25T10:25:14.384Z",
    "dateUpdated": "2026-10-24T14:09:55.095Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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