{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-40320",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-40320"
  ],
  "published": "2025-12-08T00:47:38Z",
  "summary": "smb: client: fix potential cfid UAF in smb2_query_info_compound",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix potential cfid UAF in smb2_query_info_compound\n\nWhen smb2_query_info_compound() retries, a previously allocated cfid may\nhave been freed in the first attempt.\nBecause cfid wasn't reset on replay, later cleanup could act on a stale\npointer, leading to a potential use-after-free.\n\nReinitialize cfid to NULL under the replay label.\n\nExample trace (trimmed):\n\nrefcount_t: underflow; use-after-free.\nWARNING: CPU: 1 PID: 11224 at ../lib/refcount.c:28 refcount_warn_saturate+0x9c/0x110\n[...]\nRIP: 0010:refcount_warn_saturate+0x9c/0x110\n[...]\nCall Trace:\n <TASK>\n smb2_query_info_compound+0x29c/0x5c0 [cifs f90b72658819bd21c94769b6a652029a07a7172f]\n ? step_into+0x10d/0x690\n ? __legitimize_path+0x28/0x60\n smb2_queryfs+0x6a/0xf0 [cifs f90b72658819bd21c94769b6a652029a07a7172f]\n smb311_queryfs+0x12d/0x140 [cifs f90b72658819bd21c94769b6a652029a07a7172f]\n ? kmem_cache_alloc+0x18a/0x340\n ? getname_flags+0x46/0x1e0\n cifs_statfs+0x9f/0x2b0 [cifs f90b72658819bd21c94769b6a652029a07a7172f]\n statfs_by_dentry+0x67/0x90\n vfs_statfs+0x16/0xd0\n user_statfs+0x54/0xa0\n __do_sys_statfs+0x20/0x50\n do_syscall_64+0x58/0x80",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/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-2025-40320"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/939c4e33005e2a56ea8fcedddf0da92df864bd3b"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/327f89c21601ebb7889f8c97754b76f08ce95a0c"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/b556c278d43f4707a9073ca74d55581b4f279806"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/5c76f9961c170552c1d07c830b5e145475151600"
    }
  ],
  "database_specific": {
    "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": 9.8,
      "cvss_v3_severity": "Critical",
      "scenario": "AV:N - Both halves of the bug are driven entirely by a remote SMB peer \u2014 the server decides when `compound_send_recv()` returns the replayable error (`-EAGAIN`/`-ECONNABORTED`) that reaches `replay_again:`, and it sends the SMB2 lease-break that makes `cached_dir_lease_break()` drop the cfid's last reference and free it. A malicious/compromised file server or an on-path attacker against an SMB session without signing can reach this over the network or WAN.\nAC:L - The server has deterministic control of every precondition: it triggers the replayable error, times the lease break that frees the cfid, and fails its second CREATE so `open_cached_dir()` returns without resetting `*ret_cfid`, leaving the dangling pointer guaranteed. No memory layout or timing condition outside the attacker's control is required, and the replay backoff plus a full round trip give a generous heap-grooming window.\nPR:N - The attacker is the remote SMB server or an on-path attacker and holds no privileges or credentials on the victim system. The client-side entry points (`statfs`, `getxattr`, `listxattr`) need only an unprivileged user and in practice fire unprompted from `df`, monitoring agents and container runtimes.\nUI:N - The CIFS mount is a standing deployment condition (fstab/autofs/automount in enterprise and NAS setups), not a per-attempt victim action; once it exists the server drives the entire sequence itself. It only needs to wait for a routine `statfs()`/xattr operation, which recurs continuously without any user acting.\nS:U - The use-after-free corrupts kernel heap memory within the same kernel security authority as the vulnerable cifs client code. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - On replay the stale `cfid->fid.persistent_fid` and `volatile_fid` are read from freed slab memory and transmitted verbatim to the attacker's server in the SMB2 QUERY_INFO request, a repeatable kernel-heap infoleak usable to defeat KASLR. Controlling the reallocated object escalates this to arbitrary kernel memory disclosure.\nI:H - Reaching `close_cached_dir()` on the dangling pointer runs `list_del(&cfid->entry)` with attacker-supplied `next`/`prev` (classic unlink arbitrary write), `cfid->cfids->num_entries--`, `dput()` on a forged dentry, and `kfree(cfid->path)` plus an arbitrary-free loop over the dirents list. Together these yield arbitrary write and arbitrary free, sufficient for control-flow hijack and privilege escalation.\nA:H - The reported trace shows `refcount_t: underflow; use-after-free` with a WARNING in `refcount_warn_saturate()` reached from `smb2_query_info_compound()` via `statfs`. Operating on the freed object readily oopses or panics the kernel, and the server can retrigger it at will."
    }
  }
}