{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-89674",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2026-89674"
  ],
  "published": "2026-09-11T19:47:07Z",
  "summary": "nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget\n\nThe XDR buffer size calculation in nfsd4_ff_encode_layoutget() has\nmultiple errors that can result in either an out-of-bounds write or\nleaking uninitialized kernel memory to the client:\n\n - fh_len doesn't account for XDR padding on the file handle data\n - uid and gid lengths use \"8 + len\" but xdr_encode_opaque() actually\n   writes \"4 + xdr_align_size(len)\" bytes\n - ds_len omits the flags and stats_collect_hint fields (8 bytes),\n   while len's header constant overestimates by 8 bytes -- these\n   partially cancel but leave a net mismatch\n\nThe worst case occurs with short strings (e.g. uid=0, gid=0 with an\nodd-sized file handle), where the function writes up to 5 bytes past\nthe reserved XDR buffer. Conversely, when string lengths happen to be\n4-byte aligned, the reservation is too large and stale buffer content\nis sent to the client.\n\nFix this by breaking out every encoded field explicitly in the ds_len\ncalculation, using xdr_align_size() for all variable-length opaque\nfields, and correcting the header constants.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
      },
      "versions": [
        "1:6.1.47-1+rpt4"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-2712",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v6",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v8",
            "binary_version": "1:6.1.47-1+rpt4"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.1.47-1+rpt4": {
            "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e",
            "upstream_version": "6.1.47",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.1.188",
            "compiled_filter": false
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-89674"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/3a7fd224df0fbb42167eb1b77be45d72fe0b1098"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/29e4478e2ed5a227e8f0c33cacb91bf227cedd47"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/65a72b721943618eeb3a41c8b36e915591f3f83f"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/bee826c00ac900473f91306f1f3e5a5a81fd4a74"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/e7d9d23ecd9172f05b09bb678ff22db8e361c428"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/0380129b1373c437eb35401a174671c8888f4b80"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c81cef6a805dec266c10fc4f83c93d6fcf1a2b43"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/f9868174af49d207fbaf0c5e055d088a983684af"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-09-14T12:06:03Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 9.8,
      "cvss_v3_severity": "Critical",
      "scenario": "AV:N - The bug is in nfsd's pNFS flexfile LAYOUTGET encoder (nfsd4_ff_encode_layoutget). A remote NFSv4.1 client reaches it over TCP/2049 via COMPOUND SEQUENCE, PUTFH, OPEN, and LAYOUTGET on the in-kernel NFS server.\nAC:L - A client that can OPEN a file on a flexfile pNFS export issues LAYOUTGET and hits the miscalculated xdr_reserve_space length. Root-owned files yield uid/gid \"0\", and PUTFH may append 1-3 bytes ignored by fh_verify so fh.size is odd; no race is required.\nPR:N - Typical nfsd deployments accept AUTH_SYS/AUTH_NULL without cryptographic authentication. Any host allowed by the export ACL can EXCHANGE_ID/CREATE_SESSION, PUTFH/OPEN, and LAYOUTGET; no local account on the NFS server is required.\nUI:N - The attacking NFS client drives the compounds that open a file and request a flexfile layout. No victim user action such as mounting a filesystem or opening a file on the server is required.\nS:U - The out-of-bounds write and kernel-memory leak occur in the NFS server host's XDR reply buffer. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - When the reservation is too large, stale uninitialized kernel bytes in the RPC reply are sent to the client. The matching out-of-bounds write is kernel memory corruption that can be leveraged for information disclosure per CVSS kernel guidance.\nI:H - Worst case the encoder writes up to 5 bytes past the xdr_reserve_space region, including across a reply-page boundary into adjacent kernel memory. Kernel CNA guidance scores out-of-bounds writes as High integrity impact.\nA:H - A write past the current XDR page (xdr->end) into an unmapped or unrelated page oopses or panics nfsd. The attacker can pad prior COMPOUND ops to place the LAYOUTGET encode at a page boundary and repeat the request to deny service."
    }
  }
}