CVE-2026-53341 (GCVE-0-2026-53341)
Vulnerability from cvelistv5
Published
2026-07-01 13:32
Modified
2026-08-05 12:35
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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 dereferencing an invalid address.
References
Impacted products
Vendor Product Version
Linux Linux Version: 620c266f394932e5decc4b34683a75dfc59dc2f4
Version: 620c266f394932e5decc4b34683a75dfc59dc2f4
Version: 620c266f394932e5decc4b34683a75dfc59dc2f4
Version: 620c266f394932e5decc4b34683a75dfc59dc2f4
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/fhandle.c",
            "fs/mount.h",
            "fs/namespace.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "15ea8dc42a02259d49dee38a658d40f60fcd75ed",
              "status": "affected",
              "version": "620c266f394932e5decc4b34683a75dfc59dc2f4",
              "versionType": "git"
            },
            {
              "lessThan": "32138633e51e6db59e474765cf93268c92b42888",
              "status": "affected",
              "version": "620c266f394932e5decc4b34683a75dfc59dc2f4",
              "versionType": "git"
            },
            {
              "lessThan": "a8ed2c29fcfdac78db96c9da4e659c8a513f2a94",
              "status": "affected",
              "version": "620c266f394932e5decc4b34683a75dfc59dc2f4",
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            {
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              "status": "affected",
              "version": "620c266f394932e5decc4b34683a75dfc59dc2f4",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/fhandle.c",
            "fs/mount.h",
            "fs/namespace.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.11"
            },
            {
              "lessThan": "6.11",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.95",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.36",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.13",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.95",
                  "versionStartIncluding": "6.11",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.36",
                  "versionStartIncluding": "6.11",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.0.13",
                  "versionStartIncluding": "6.11",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1",
                  "versionStartIncluding": "6.11",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfhandle: fix UAF due to unlocked -\u003emnt_ns read in may_decode_fh()\n\nmay_decode_fh() accesses mount::mnt_ns without holding any locks; that\nmeans the mount can concurrently be unmounted, and the mnt_namespace can\nconcurrently be freed after an RCU grace period.\n\nThis race can happens as follows, assuming that the mount point was\ncreated by open_tree(..., OPEN_TREE_CLONE):\n\nthread 1            thread 2            RCU\n                    __do_sys_open_by_handle_at\n                      do_handle_open\n                        handle_to_path\n                          may_decode_fh\n                            is_mounted\n                              [mount::mnt_ns access]\n                            [mount::mnt_ns access]\n__do_sys_close\n  fput_close_sync\n    __fput\n      dissolve_on_fput\n        umount_tree\n        class_namespace_excl_destructor\n          namespace_unlock\n            free_mnt_ns\n              mnt_ns_tree_remove\n                call_rcu(mnt_ns_release_rcu)\n                                        mnt_ns_release_rcu\n                                          mnt_ns_release\n                                            kfree\n                            [mnt_namespace::user_ns access] **UAF**\n\nFix it by taking rcu_read_lock() around the mount::mnt_ns access, like\nin __prepend_path().\nAdditionally, document the semantics of mount::mnt_ns, and use WRITE_ONCE()\nfor writers that can race with lockless readers.\n\nThis bug is unreachable unless one of the following is set:\n\n - CONFIG_PREEMPTION\n - CONFIG_RCU_STRICT_GRACE_PERIOD\n\nbecause it requires an RCU grace period to happen during a syscall without\nan explicit preemption.\n\nThis doesn\u0027t seem to have interesting security impact; worst-case, it could\nleak the result of an integer comparison to userspace (from the level\ncheck in cap_capable()), cause an endless loop, or crash the kernel by\ndereferencing an invalid address."
        }
      ],
      "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 - The vulnerable code is reached through local syscalls, primarily `open_by_handle_at()` racing with close/fput of a mount file created by `open_tree(..., OPEN_TREE_CLONE)`. There is no network or adjacent attack path.\nAC:L - The attacker can control both sides of the race by running concurrent local threads that call `open_by_handle_at()` and close the cloned mount file. Although the bug requires preemption or strict RCU grace periods, those are reasonable kernel configurations and the race is attacker-driven.\nPR:L - The path requires namespace-relative capabilities such as `CAP_SYS_ADMIN` and `CAP_DAC_READ_SEARCH`, which an unprivileged local user can obtain inside a user namespace on systems where unprivileged user namespaces are enabled. It does not require real init-namespace root.\nUI:N - No victim action is required; the attacker directly invokes the relevant syscalls and controls the racing threads. The mount clone, handle input, and close operation are all attacker initiated.\nS:U - The vulnerability affects kernel VFS/mount namespace state within the same security authority. It is a local kernel memory-safety issue, not a VM escape or cross-scope boundary bypass.\nC:H - The bug is a kernel use-after-free of `struct mnt_namespace`, followed by dereferencing reclaimed memory through `mnt_ns-\u003euser_ns` and capability-walk fields. Per the higher-severity rule for kernel UAFs, this is scored as high confidentiality impact.\nI:H - The immediate operation is a stale read in an authorization check, but reclaimed kernel heap contents can influence capability-check control flow and UAFs are treated as potentially exploitable memory corruption. Under the required uncertainty rule, integrity impact is high.\nA:H - The stale `mnt_namespace` dereference can crash the kernel, loop indefinitely, or otherwise destabilize the system. A local attacker can repeatedly trigger the race, so availability impact is high."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:35:02.388Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/15ea8dc42a02259d49dee38a658d40f60fcd75ed"
        },
        {
          "url": "https://git.kernel.org/stable/c/32138633e51e6db59e474765cf93268c92b42888"
        },
        {
          "url": "https://git.kernel.org/stable/c/a8ed2c29fcfdac78db96c9da4e659c8a513f2a94"
        },
        {
          "url": "https://git.kernel.org/stable/c/40ab6644b99685755f740b872c00ef40d9aa870e"
        }
      ],
      "title": "fhandle: fix UAF due to unlocked -\u003emnt_ns read in may_decode_fh()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-53341",
    "datePublished": "2026-07-01T13:32:22.873Z",
    "dateReserved": "2026-06-09T07:44:35.399Z",
    "dateUpdated": "2026-08-05T12:35:02.388Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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