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GHSA-38FM-JC3C-V2PM

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

Details

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

namespace: keep the lock on a mount that a propagated copy is moved beneath

attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the owner of a user namespace to replace its locked /proc or its root. The mount beneath takes on the job of covering the underlying mountpoint allowing the top mount to be unmounted.

Consider two mount namespaces:

(H) The host H has a shared mount P with a secret in P/d (Z) Z is a user namespace made from M. Its copy of P receives propagation from the host's P and its copy of M's cover on P/d is locked Z's owner must not get to see P/d.

Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands beneath (Z)'s locked cover. The locked property is transfered from (Z)'s cover to the copy of X propagated beneath it. The cover is now unlocked.

Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the covering mount is left unlocked on top of P/d. (Z) can now unmount it:

Z: umount2(P/d)             = EINVAL            /* the cover is locked */
H: mount X on P/d, umount X                     /* both propagate into Z /*
Z: umount2(P/d)             = 0                 /* the cover is now unlocked */
Z: read P/d/secret          = "covered-by-root" /* secret revealed */

So only transfer the locked property to the mount beneath for mounts the caller has placed. A propagated copy that lands beneath a locked mount is locked as well so that the mount at the bottom of the stack carries a lock the way every check expects. The mount on top of it remains locked to ensure that it keeps covering even if the propagated mount is unmounted again.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98976"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-23T13:17:19Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: keep the lock on a mount that a propagated copy is moved beneath\n\nattach_recursive_mnt() transfers MNT_LOCKED from the top mount to the\nmount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the\nowner of a user namespace to replace its locked /proc or its root. The\nmount beneath takes on the job of covering the underlying mountpoint\nallowing the top mount to be unmounted.\n\nConsider two mount namespaces:\n\n(H) The host H has a shared mount P with a secret in P/d\n(Z) Z is a user namespace made from M. Its copy of P receives\n    propagation from the host\u0027s P and its copy of M\u0027s cover on P/d is\n    locked Z\u0027s owner must not get to see P/d.\n\nNow (H) mounts X on P/d. This propagates into (Z). The copy of X lands\nbeneath (Z)\u0027s locked cover. The locked property is transfered from (Z)\u0027s\ncover to the copy of X propagated beneath it. The cover is now unlocked.\n\nNow (H) unmounts X again. The copy of X in (Z) gets unmounted and the\ncovering mount is left unlocked on top of P/d. (Z) can now unmount it:\n\n    Z: umount2(P/d)             = EINVAL            /* the cover is locked */\n    H: mount X on P/d, umount X                     /* both propagate into Z /*\n    Z: umount2(P/d)             = 0                 /* the cover is now unlocked */\n    Z: read P/d/secret          = \"covered-by-root\" /* secret revealed */\n\nSo only transfer the locked property to the mount beneath for mounts the\ncaller has placed. A propagated copy that lands beneath a locked mount\nis locked as well so that the mount at the bottom of the stack carries a\nlock the way every check expects. The mount on top of it remains locked\nto ensure that it keeps covering even if the propagated mount is\nunmounted again.",
  "id": "GHSA-38fm-jc3c-v2pm",
  "modified": "2026-10-23T15:31:33Z",
  "published": "2026-10-23T15:31:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98976"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f1f0c24ca701d7d3061c7f69f7450f1734c11745"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-98976 (GCVE-0-2026-98976)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:19 – Updated: 2026-10-24 14:09

Title

namespace: keep the lock on a mount that a propagated copy is moved beneath

Summary

In the Linux kernel, the following vulnerability has been resolved: namespace: keep the lock on a mount that a propagated copy is moved beneath attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the owner of a user namespace to replace its locked /proc or its root. The mount beneath takes on the job of covering the underlying mountpoint allowing the top mount to be unmounted. Consider two mount namespaces: (H) The host H has a shared mount P with a secret in P/d (Z) Z is a user namespace made from M. Its copy of P receives propagation from the host's P and its copy of M's cover on P/d is locked Z's owner must not get to see P/d. Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands beneath (Z)'s locked cover. The locked property is transfered from (Z)'s cover to the copy of X propagated beneath it. The cover is now unlocked. Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the covering mount is left unlocked on top of P/d. (Z) can now unmount it: Z: umount2(P/d) = EINVAL /* the cover is locked */ H: mount X on P/d, umount X /* both propagate into Z /* Z: umount2(P/d) = 0 /* the cover is now unlocked */ Z: read P/d/secret = "covered-by-root" /* secret revealed */ So only transfer the locked property to the mount beneath for mounts the caller has placed. A propagated copy that lands beneath a locked mount is locked as well so that the mount at the bottom of the stack carries a lock the way every check expects. The mount on top of it remains locked to ensure that it keeps covering even if the propagated mount is unmounted again.

Severity

7.8 (High)


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

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 7061 records in the last 180 days details

References

2 references

URL	Tags
https://git.kernel.org/stable/c/f1f0c24ca701d7d30…
https://git.kernel.org/stable/c/d74d66aa708ccf2bc…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: c62a4766937edec2962d52e583276b459b739f2d , < f1f0c24ca701d7d3061c7f69f7450f1734c11745 (git) Affected: c62a4766937edec2962d52e583276b459b739f2d , < d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4 (git)
Linux	Linux	Affected: 7.1 Unaffected: 0 , < 7.1 (semver) Unaffected: 7.2.11 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/namespace.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "lessThan": "f1f0c24ca701d7d3061c7f69f7450f1734c11745",
              "status": "affected",
              "version": "c62a4766937edec2962d52e583276b459b739f2d",
              "versionType": "git"
            },
            {
              "lessThan": "d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4",
              "status": "affected",
              "version": "c62a4766937edec2962d52e583276b459b739f2d",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/namespace.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.1"
            },
            {
              "lessThan": "7.1",
              "status": "unaffected",
              "version": "0",
              "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": "7.2.11",
                  "versionStartIncluding": "7.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "7.1",
                  "vulnerable": true
                }
              ],
              "negate": false,
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      "descriptions": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: keep the lock on a mount that a propagated copy is moved beneath\n\nattach_recursive_mnt() transfers MNT_LOCKED from the top mount to the\nmount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the\nowner of a user namespace to replace its locked /proc or its root. The\nmount beneath takes on the job of covering the underlying mountpoint\nallowing the top mount to be unmounted.\n\nConsider two mount namespaces:\n\n(H) The host H has a shared mount P with a secret in P/d\n(Z) Z is a user namespace made from M. Its copy of P receives\n    propagation from the host\u0027s P and its copy of M\u0027s cover on P/d is\n    locked Z\u0027s owner must not get to see P/d.\n\nNow (H) mounts X on P/d. This propagates into (Z). The copy of X lands\nbeneath (Z)\u0027s locked cover. The locked property is transfered from (Z)\u0027s\ncover to the copy of X propagated beneath it. The cover is now unlocked.\n\nNow (H) unmounts X again. The copy of X in (Z) gets unmounted and the\ncovering mount is left unlocked on top of P/d. (Z) can now unmount it:\n\n    Z: umount2(P/d)             = EINVAL            /* the cover is locked */\n    H: mount X on P/d, umount X                     /* both propagate into Z /*\n    Z: umount2(P/d)             = 0                 /* the cover is now unlocked */\n    Z: read P/d/secret          = \"covered-by-root\" /* secret revealed */\n\nSo only transfer the locked property to the mount beneath for mounts the\ncaller has placed. A propagated copy that lands beneath a locked mount\nis locked as well so that the mount at the bottom of the stack carries a\nlock the way every check expects. The mount on top of it remains locked\nto ensure that it keeps covering even if the propagated mount is\nunmounted again."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerable path is local mount propagation: mount(2) reaches do_mount()-\u003epath_mount()-\u003edo_new_mount()-\u003edo_new_mount_fc()-\u003edo_add_mount()-\u003egraft_tree()-\u003eattach_recursive_mnt(), after which Z uses local umount2()/open(); no network protocol carries input.\nAC:H - Exploitation requires a shared P, a manager namespace with a locked cover at P/d, and a privileged host process mounting and unmounting X there after Z is cloned. Z is only a slave receiver and cannot propagate upward or induce that lifecycle itself.\nPR:L - unshare(CLONE_NEWUSER|CLONE_NEWNS) lets an ordinary local creator own Z; can_umount()-\u003emay_mount() requires only CAP_SYS_ADMIN in Z\u0027s owning user namespace. The privileged host mount lifecycle is an external prerequisite, not attacker-held privilege.\nUI:N - The required host mount lifecycle can occur through automated mount management without a human being induced to act. After it occurs, the Z task itself invokes umount2(P/d) and accesses the exposed path.\nS:C - lock_mnt_tree() sets MNT_LOCKED specifically when copying a more privileged mount tree into Z; clearing it exposes resources hidden by the manager namespace to the confined Z task, crossing that namespace sandbox boundary.\nC:H - The faulty attach_recursive_mnt() clears MNT_LOCKED on q; after propagate_umount() removes X\u0027s copy, umount2(P/d) exposes the entire underlying subtree, as demonstrated by opening P/d/secret, rather than leaking only bounded metadata.\nI:H - Removing the cover also permits open/write/rename/unlink operations on the whole underlying subtree wherever the confined task\u0027s kernel UID has DAC access, defeating mount-based read-only or masking policy and allowing arbitrary modification of protected files there.\nA:H - When the locked cover protects an attacker-UID-owned service or application tree, the same exposed-path primitive permits wholesale deletion or replacement of its files, causing persistent loss of availability for those protected resources."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:09:46.343Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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        {
          "url": "https://git.kernel.org/stable/c/f1f0c24ca701d7d3061c7f69f7450f1734c11745"
        },
        {
          "url": "https://git.kernel.org/stable/c/d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4"
        }
      ],
      "title": "namespace: keep the lock on a mount that a propagated copy is moved beneath",
      "x_generator": {
        "engine": "bippy-1.2.0"
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    }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98976",
    "datePublished": "2026-10-23T12:19:49.363Z",
    "dateReserved": "2026-09-25T10:25:14.383Z",
    "dateUpdated": "2026-10-24T14:09:46.343Z",
    "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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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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