fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh()

{
  "id": "a5abce6f550c66d66fab15e0ddade68743819caf886fd1ad8bb52cf21def7baf",
  "url": "https://osv.dev/vulnerability/CVE-2026-53341",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh() may_decode_fh() accesses mount::mnt_ns without holding any locks; that means the mount can concurrently be unmounted, and the mnt_namespace can concurrently be freed after an RCU grace period. This race can happens as follows, assuming that the mount point was created by open_tree(..., OPEN_TREE_CLONE): thread 1 thread 2 RCU __do_sys_open_by_handle_at do_handle_open handle_to_path may_decode_fh is_mounted [mount::mnt_ns access] [mount::mnt_ns access] __do_sys_close fput_close_sync __fput dissolve_on_fput umount_tree class_namespace_excl_destructor namespace_unlock free_mnt_ns mnt_ns_tree_remove call_rcu(mnt_ns_release_rcu) mnt_ns_release_rcu mnt_ns_release kfree [mnt_namespace::user_ns access] **UAF** Fix it by taking rcu_read_lock() around the mount::mnt_ns access, like in __prepend_path(). Additionally, document the semantics of mount::mnt_ns, and use WRITE_ONCE() for writers that can race with lockless readers. This bug is unreachable unless one of the following is set: - CONFIG_PREEMPTION - CONFIG_RCU_STRICT_GRACE_PERIOD because it requires an RCU grace period to happen during a syscall without an explicit preemption. This doesn't seem to have interesting security impact; worst-case, it could leak the result of an integer comparison to userspace (from the level check in cap_capable()), cause an endless loop, or crash the kernel by dereferen",
    "evidence": "osv:CVE-2026-53341",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.95",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.36",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.13",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-53341",
      "aliases": [
        "CVE-2026-53341"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "15ea8dc42a02259d49dee38a658d40f60fcd75ed"
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                {
                  "fixed": "32138633e51e6db59e474765cf93268c92b42888"
                },
                {
                  "fixed": "a8ed2c29fcfdac78db96c9da4e659c8a513f2a94"
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                {
                  "fixed": "40ab6644b99685755f740b872c00ef40d9aa870e"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53341.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.11.0"
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                  "fixed": "6.12.95"
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            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.13.0"
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                {
                  "fixed": "6.18.36"
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              ]
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            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
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                {
                  "fixed": "7.0.13"
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53341.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:36.639170365Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/15ea8dc42a02259d49dee38a658d40f60fcd75ed",
        "https://git.kernel.org/stable/c/32138633e51e6db59e474765cf93268c92b42888",
        "https://git.kernel.org/stable/c/40ab6644b99685755f740b872c00ef40d9aa870e",
        "https://git.kernel.org/stable/c/a8ed2c29fcfdac78db96c9da4e659c8a513f2a94",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53341.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-53341",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53341.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-53341",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 503981,
  "published_at": "2026-07-01T13:32:22.873+00:00"
}