CVE-2026-89674 (GCVE-0-2026-89674)
Vulnerability from cvelistv5
Published
2026-09-11 19:45
Modified
2026-10-19 08:50
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget The XDR buffer size calculation in nfsd4_ff_encode_layoutget() has multiple errors that can result in either an out-of-bounds write or leaking uninitialized kernel memory to the client: - fh_len doesn't account for XDR padding on the file handle data - uid and gid lengths use "8 + len" but xdr_encode_opaque() actually writes "4 + xdr_align_size(len)" bytes - ds_len omits the flags and stats_collect_hint fields (8 bytes), while len's header constant overestimates by 8 bytes -- these partially cancel but leave a net mismatch The worst case occurs with short strings (e.g. uid=0, gid=0 with an odd-sized file handle), where the function writes up to 5 bytes past the reserved XDR buffer. Conversely, when string lengths happen to be 4-byte aligned, the reservation is too large and stale buffer content is sent to the client. Fix this by breaking out every encoded field explicitly in the ds_len calculation, using xdr_align_size() for all variable-length opaque fields, and correcting the header constants.
References
Impacted products
Vendor Product Version
Linux Linux Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
Version: 9b9960a0ca4773e21c4b153ed355583946346b25
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/flexfilelayoutxdr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "versionType": "git"
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            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/flexfilelayoutxdr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.8"
            },
            {
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "5.10.270",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.188",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.109",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.270",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.221",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.188",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.157",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.109",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.50",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "4.8",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u0027t 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\u0027s 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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is in nfsd\u0027s 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\u0027s 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-\u003eend) 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."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:50:47.609Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/3a7fd224df0fbb42167eb1b77be45d72fe0b1098"
        },
        {
          "url": "https://git.kernel.org/stable/c/29e4478e2ed5a227e8f0c33cacb91bf227cedd47"
        },
        {
          "url": "https://git.kernel.org/stable/c/65a72b721943618eeb3a41c8b36e915591f3f83f"
        },
        {
          "url": "https://git.kernel.org/stable/c/bee826c00ac900473f91306f1f3e5a5a81fd4a74"
        },
        {
          "url": "https://git.kernel.org/stable/c/e7d9d23ecd9172f05b09bb678ff22db8e361c428"
        },
        {
          "url": "https://git.kernel.org/stable/c/0380129b1373c437eb35401a174671c8888f4b80"
        },
        {
          "url": "https://git.kernel.org/stable/c/c81cef6a805dec266c10fc4f83c93d6fcf1a2b43"
        },
        {
          "url": "https://git.kernel.org/stable/c/f9868174af49d207fbaf0c5e055d088a983684af"
        }
      ],
      "title": "nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89674",
    "datePublished": "2026-09-11T19:45:58.883Z",
    "dateReserved": "2026-09-11T19:38:34.746Z",
    "dateUpdated": "2026-10-19T08:50:47.609Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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