{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21994",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21994"
  ],
  "published": "2025-04-02T13:59:32Z",
  "summary": "ksmbd: fix incorrect validation for num_aces field of smb_acl",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix incorrect validation for num_aces field of smb_acl\n\nparse_dcal() validate num_aces to allocate posix_ace_state_array.\n\nif (num_aces > ULONG_MAX / sizeof(struct smb_ace *))\n\nIt is an incorrect validation that we can create an array of size ULONG_MAX.\nsmb_acl has ->size field to calculate actual number of aces in request buffer\nsize. Use this to check invalid num_aces.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H"
    }
  ],
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        "per_version": {
          "1:6.12.19-1+rpt1~bpo12+1": {
            "linux_commit": "121c2c384b9c2f4790ffb31b2cd25c7d75c8fda0",
            "upstream_version": "6.12.19",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.21"
          },
          "1:6.12.19-1+rpt1": {
            "linux_commit": "121c2c384b9c2f4790ffb31b2cd25c7d75c8fda0",
            "upstream_version": "6.12.19",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.21"
          },
          "1:6.12.20-1+rpt1": {
            "linux_commit": "cd231d4775b14f228606c09f219b48308f6ab3aa",
            "upstream_version": "6.12.20",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.21"
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-21994"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c3a3484d9d31b27a3db0fab91fcf191132d65236"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/9c4e202abff45f8eac17989e549fc7a75095f675"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/d0f87370622a853b57e851f7d5a5452b72300f19"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a4cb17797a5d241f1e509cb5b46ed95a80c2f5fd"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/f6a6721802ac2f12f4c1bbe839a4c229b61866f2"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/1b8b67f3c5e5169535e26efedd3e422172e2db64"
    }
  ],
  "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": 7.6,
      "cvss_v3_severity": "High",
      "scenario": "AV:N - ksmbd is the in-kernel SMB server listening on TCP/445, and the malformed `num_aces`/DACL arrives directly in an SMB2_SET_INFO (SMB2_O_INFO_SECURITY) or SMB2_CREATE SD_BUFFER request payload. No local access to the target is needed at any point.\nAC:L - The attacker simply sets the 16/32-bit `num_aces` field of the DACL header to a large value while keeping `pdacl->size` minimal; the oversized allocations follow deterministically on the first request with no race, no memory-layout dependency, and no non-default configuration beyond ksmbd being enabled.\nPR:L - `smb2_set_info()` is reached only after SMB2 session setup, and it additionally requires `KSMBD_TREE_CONN_FLAG_WRITABLE` on the tree connect plus a valid file handle, so any ordinary share account (or the guest account where the share permits it) suffices \u2014 but unauthenticated access does not.\nUI:N - The attacker completes the session setup, tree connect, open and SET_INFO sequence entirely on its own. No administrator or client-side victim action is involved.\nS:U - The oversized allocations and the misparsed ACL stay entirely within the kernel's own security authority on the SMB server host; no VM, IOMMU, container, or sandbox boundary is crossed.\nC:L - The same commit removes a `sid.sub_auth[num_subauth - 1]` negative-index read that, with `num_subauth == 0`, reads the four bytes preceding `sub_auth` and feeds them to `sid_to_id()` and the group-SID test. The read is strictly bounded to 4 bytes that lie inside the client's own request buffer (`end_of_acl` is validated by `ksmbd_smb2_check_message()`), so it is a limited misread rather than an arbitrary kernel-memory disclosure.\nI:L - `parse_dacl()`'s output is applied to the file through `set_posix_acl()` and `notify_change()` in `set_info_sec()`, so an ACL parsed from an unvalidated ACE count and an out-of-bounds `sub_auth[-1]` value yields on-disk permissions and uid/gid mappings that do not correspond to the descriptor sent. This is bounded metadata corruption on files the attacker can already write; the `num_aces`-sized `ppace` and `posix_ace_state_array` writes remain in bounds and the `init_acl_state()` `int` truncation is unreachable because the paired `kmalloc_array()` fails first, so there is no arbitrary-write primitive.\nA:H - A ~120-byte request forces up to ~19 MB of high-order `GFP_KERNEL` allocations (4 \u00d7 ~4 MB `posix_ace_state_array` plus ~2.8 MB `ppace`), a ~200,000\u00d7 amplification, and ksmbd's 256-slot `ksmbd-io` workqueue lets a few connections drive gigabytes of concurrent order-8/order-10 allocation pressure \u2014 producing direct-reclaim/compaction stalls, page-allocation-failure splats (fatal under `panic_on_warn`), and OOM kills that take down the host, which is especially severe on the NAS, router, and embedded devices where ksmbd is commonly deployed."
    }
  }
}