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  "id": "RPI-CVE-2025-40203",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-40203"
  ],
  "published": "2025-11-12T22:01:07Z",
  "summary": "listmount: don't call path_put() under namespace semaphore",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nlistmount: don't call path_put() under namespace semaphore\n\nMassage listmount() and make sure we don't call path_put() under the\nnamespace semaphore. If we put the last reference we're fscked.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-40203"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/659874b7ee4976ad9ce476e07fd36bc67b3537f1"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/9c80da26fda2fdcaac7f92b5908875b3108830ff"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c1f86d0ac322c7e77f6f8dbd216c65d39358ffc0"
    }
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    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T12:19:11Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The vulnerability is reached only through the `listmount(2)` system call in fs/namespace.c; there is no remote or adjacent-network path to `do_listmount()`. Exploitation requires the ability to execute syscalls on the target, i.e. local access.\nAC:L - The attacker controls both sides of the race \u2014 it holds the extra path reference via `listmount()` while a `CLONE_FS` sibling thread moves `fs->root` off a lazily-unmounted mount, deterministically making the in-syscall `path_put()` the final reference. The setup (unshare, tmpfs mount, chroot, `umount2(MNT_DETACH)`) is scripted and retryable without limit.\nPR:L - `listmount(2)` requires no capability at all for the caller's own mount namespace, and the mount/chroot/lazy-umount setup is obtainable by any unprivileged user via `unshare -Ur` since CAP_SYS_ADMIN/CAP_SYS_CHROOT are granted inside a user namespace. No real root in the init namespace is needed.\nUI:N - The attacking process performs every step itself \u2014 namespace creation, mount setup, and the concurrent `listmount()`/`chroot()` race. No victim action or cooperation is involved.\nS:U - The corrupted state (`struct mount`, `struct mountpoint`, `struct dentry`, `namespace_sem`) and the resulting impact all live within the kernel's own security authority. No hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - The final `mntput_no_expire()` tears down mounts, frees `struct mountpoint`, and destroys dentries/inodes while only the read side of `namespace_sem` is held, so concurrent readers (other `listmount()`/`statmount()`/propagation walkers that legitimately hold the read lock and expect a stable topology) can traverse freed objects \u2014 a use-after-free giving an attacker-influenceable kernel-memory read primitive via slab reuse.\nI:H - The same violated invariant permits mount-tree list surgery (`list_del(&mnt->mnt_instance)`, `unhash_mnt()`, child reparenting) to race concurrent read-side traversal, yielding linked-list corruption and use-after-free writes into reallocated slab objects, which is exploitable for control-flow hijacking.\nA:H - Performing the final `path_put()` under `namespace_sem` can block or self-deadlock \u2014 inode eviction can stall indefinitely on a userspace filesystem daemon, and `__detach_mounts()`'s `down_write(&namespace_sem)` on an already read-held semaphore deadlocks \u2014 hanging every mount, umount, statmount, and listmount on the system; the same UAF also reliably oopses the kernel."
    }
  }
}