Vulnerability-Lookup

GHSA-G7V4-CHCG-VJ96

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33

Details

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

fhandle: reject detached mounts in capable_wrt_mount()

The recent fhandle RCU fix moved the mount namespace capability check into capable_wrt_mount(), so a non-NULL mnt_namespace survives the ns_capable() dereference. The helper still assumes the later READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh() checked is_mounted() first.

That assumption is not stable. A detached mount from open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while open_by_handle_at() is between those checks, and umount_tree() can clear mount->mnt_ns. If the helper observes NULL, it dereferences mnt_ns->user_ns and panics.

Return false when the RCU read observes a detached mount. This keeps the relaxed permission path conservative: a mount no longer attached to a namespace cannot authorize open_by_handle_at() access.

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-2026-72034"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:21:12Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfhandle: reject detached mounts in capable_wrt_mount()\n\nThe recent fhandle RCU fix moved the mount namespace capability check\ninto capable_wrt_mount(), so a non-NULL mnt_namespace survives the\nns_capable() dereference. The helper still assumes the later\nREAD_ONCE(mount-\u003emnt_ns) must be non-NULL because may_decode_fh()\nchecked is_mounted() first.\n\nThat assumption is not stable. A detached mount from\nopen_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while\nopen_by_handle_at() is between those checks, and umount_tree() can\nclear mount-\u003emnt_ns. If the helper observes NULL, it dereferences\nmnt_ns-\u003euser_ns and panics.\n\nReturn false when the RCU read observes a detached mount. This keeps\nthe relaxed permission path conservative: a mount no longer attached\nto a namespace cannot authorize open_by_handle_at() access.",
  "id": "GHSA-g7v4-chcg-vj96",
  "modified": "2026-08-17T06:33:06Z",
  "published": "2026-08-15T06:32:09Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72034"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/15104234c267ebe04b9f9a73e5c2179cc265ff60"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6c52226072a3c61337b1eec1799bb987748884fa"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6c732471740bc2ac9b0946134f9f551dc75f4369"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6ee183d89261bf1d1cf9f06d80a40dab8f36ee55"
    }
  ],
  "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-2026-72034 (GCVE-0-2026-72034)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:51 – Updated: 2026-08-17 05:39

Title

fhandle: reject detached mounts in capable_wrt_mount()

Summary

In the Linux kernel, the following vulnerability has been resolved: fhandle: reject detached mounts in capable_wrt_mount() The recent fhandle RCU fix moved the mount namespace capability check into capable_wrt_mount(), so a non-NULL mnt_namespace survives the ns_capable() dereference. The helper still assumes the later READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh() checked is_mounted() first. That assumption is not stable. A detached mount from open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while open_by_handle_at() is between those checks, and umount_tree() can clear mount->mnt_ns. If the helper observes NULL, it dereferences mnt_ns->user_ns and panics. Return false when the RCU read observes a detached mount. This keeps the relaxed permission path conservative: a mount no longer attached to a namespace cannot authorize open_by_handle_at() access.

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 mitre root

References

4 references

URL	Tags
https://git.kernel.org/stable/c/15104234c267ebe04…
https://git.kernel.org/stable/c/6c52226072a3c6133…
https://git.kernel.org/stable/c/6ee183d89261bf1d1…
https://git.kernel.org/stable/c/6c732471740bc2ac9…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 620c266f394932e5decc4b34683a75dfc59dc2f4 , < 15104234c267ebe04b9f9a73e5c2179cc265ff60 (git) Affected: 620c266f394932e5decc4b34683a75dfc59dc2f4 , < 6c52226072a3c61337b1eec1799bb987748884fa (git) Affected: 620c266f394932e5decc4b34683a75dfc59dc2f4 , < 6ee183d89261bf1d1cf9f06d80a40dab8f36ee55 (git) Affected: 620c266f394932e5decc4b34683a75dfc59dc2f4 , < 6c732471740bc2ac9b0946134f9f551dc75f4369 (git)
Linux	Linux	Affected: 6.11 Unaffected: 0 , < 6.11 (semver) Unaffected: 6.12.97 , ≤ 6.12.* (semver) Unaffected: 6.18.40 , ≤ 6.18.* (semver) Unaffected: 7.1.5 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/fhandle.c"
          ],
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          "vendor": "Linux",
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            {
              "lessThan": "15104234c267ebe04b9f9a73e5c2179cc265ff60",
              "status": "affected",
              "version": "620c266f394932e5decc4b34683a75dfc59dc2f4",
              "versionType": "git"
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            {
              "lessThan": "6c52226072a3c61337b1eec1799bb987748884fa",
              "status": "affected",
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              "versionType": "git"
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              "lessThan": "6ee183d89261bf1d1cf9f06d80a40dab8f36ee55",
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              "version": "620c266f394932e5decc4b34683a75dfc59dc2f4",
              "versionType": "git"
            },
            {
              "lessThan": "6c732471740bc2ac9b0946134f9f551dc75f4369",
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              "versionType": "git"
            }
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        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/fhandle.c"
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          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.11"
            },
            {
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
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              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.40",
              "versionType": "semver"
            },
            {
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              "version": "7.1.5",
              "versionType": "semver"
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            {
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      "cpeApplicability": [
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          "nodes": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.97",
                  "versionStartIncluding": "6.11",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                },
                {
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                },
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              ],
              "negate": false,
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfhandle: reject detached mounts in capable_wrt_mount()\n\nThe recent fhandle RCU fix moved the mount namespace capability check\ninto capable_wrt_mount(), so a non-NULL mnt_namespace survives the\nns_capable() dereference. The helper still assumes the later\nREAD_ONCE(mount-\u003emnt_ns) must be non-NULL because may_decode_fh()\nchecked is_mounted() first.\n\nThat assumption is not stable. A detached mount from\nopen_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while\nopen_by_handle_at() is between those checks, and umount_tree() can\nclear mount-\u003emnt_ns. If the helper observes NULL, it dereferences\nmnt_ns-\u003euser_ns and panics.\n\nReturn false when the RCU read observes a detached mount. This keeps\nthe relaxed permission path conservative: a mount no longer attached\nto a namespace cannot authorize open_by_handle_at() access."
        }
      ],
      "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 - Exploitation requires local syscalls only: open_tree(OPEN_TREE_CLONE) to obtain a detached mount fd, open_by_handle_at() to enter may_decode_fh()/capable_wrt_mount(), and close()/fput to dissolve the mount; no network, adjacent, or physical interface reaches this VFS fhandle path.\nAC:L - The attacker controls both sides of the TOCTOU race by concurrently calling open_by_handle_at() on a detached mount fd while another thread closes that fd (or a dup) to trigger dissolve_on_fput()/umount_tree() clearing mount-\u003emnt_ns, making success depend on attacker timing rather than external state.\nPR:L - The relaxed permission path requires CAP_SYS_ADMIN in the current mount namespace (may_mount/open_tree) and CAP_DAC_READ_SEARCH in the current user namespace while lacking init_user_ns CAP_DAC_READ_SEARCH; these are obtainable by an unprivileged local user via user/mount namespaces (unshare -Urn), not real init-namespace root.\nUI:N - No victim action is required; the attacker creates the detached mount, supplies the file handle, and drives the concurrent open_by_handle_at()/close race entirely through their own syscalls and threads.\nS:U - Impact is confined to kernel memory/availability within the same security authority (local/container-triggered kernel panic or namespace lifetime corruption); it does not cross a VM escape, sandbox, or IOMMU boundary per kernel CVSS scope guidance.\nC:H - The affected window (since 620c266f3949) includes unsynchronized mount::mnt_ns access that can UAF freed mnt_namespace memory before the RCU fix, and later NULL/stale namespace dereferences; per kernel guidance UAF and mount-namespace lifetime races enable arbitrary kernel memory disclosure.\nI:H - Concurrent umount_tree() clearing mount-\u003emnt_ns while capable_wrt_mount() dereferences mnt_ns-\u003euser_ns is a mount-namespace lifetime corruption bug; UAF in the same code path can be leveraged for heap corruption and arbitrary kernel writes/code execution, not merely a benign error return.\nA:H - Observing NULL or freed mnt_ns during ns_capable(mnt_ns-\u003euser_ns, CAP_SYS_ADMIN) causes a kernel oops/panic; the race is repeatable by reopening detached mounts, enabling reliable host DoS from containerized tenants on multi-tenant cloud nodes."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:39:37.172Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        },
        {
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        },
        {
          "url": "https://git.kernel.org/stable/c/6c732471740bc2ac9b0946134f9f551dc75f4369"
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      "title": "fhandle: reject detached mounts in capable_wrt_mount()",
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      }
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72034",
    "datePublished": "2026-08-15T05:51:55.739Z",
    "dateReserved": "2026-08-09T03:40:39.901Z",
    "dateUpdated": "2026-08-17T05:39:37.172Z",
    "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.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
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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GHSA-G7V4-CHCG-VJ96

CVE-2026-72034 (GCVE-0-2026-72034)

Tags

Sightings

Nomenclature