CVE-2026-89706 (GCVE-0-2026-89706)
Vulnerability from cvelistv5
Published
2026-09-11 19:46
Modified
2026-10-19 08:51
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: Reset write verifier when async COPY writeback fails Async COPY captures nn->writeverf at request time and reports it to the client via CB_OFFLOAD after the worker kthread completes. When the post-copy vfs_fsync_range() or filemap_check_wb_err() in _nfsd_copy_file_range() reports an error, the worker correctly leaves NFSD4_COPY_F_COMMITTED clear so that CB_OFFLOAD encodes wr_stable_how as NFS_UNSTABLE, but the server's write verifier is not rotated. A client that receives NFS_UNSTABLE in CB_OFFLOAD follows up with COMMIT to make the copied data durable. With the verifier unchanged, COMMIT returns the same value the client just received via CB_OFFLOAD, and the client concludes the copy is durable -- silently dropping the data whose writeback in fact failed. This violates the UNSTABLE+COMMIT durability contract (RFC 7862 section 15.1, RFC 8881 section 18.32) and matches the bug just fixed in nfsd_vfs_write() and nfsd_commit(). Rotate nn->writeverf at the writeback-failure site. The async COPY worker has no svc_rqst, so commit_reset_write_verifier() is not available here; calling nfsd_reset_write_verifier() directly mirrors the trace-less reset already used by nfsd_file_check_write_error() for the same purpose. Filter out -EAGAIN and -ESTALE, matching commit_reset_write_verifier(), since neither indicates a durable-storage failure.
References
Impacted products
Vendor Product Version
Linux Linux Version: 817c6eb975798647c4bbbfc9eb288aa413ec7f65
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d
Version: 5.10.220   ≤
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4proc.c"
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              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: Reset write verifier when async COPY writeback fails\n\nAsync COPY captures nn-\u003ewriteverf at request time and reports it to\nthe client via CB_OFFLOAD after the worker kthread completes. When\nthe post-copy vfs_fsync_range() or filemap_check_wb_err() in\n_nfsd_copy_file_range() reports an error, the worker correctly\nleaves NFSD4_COPY_F_COMMITTED clear so that CB_OFFLOAD encodes\nwr_stable_how as NFS_UNSTABLE, but the server\u0027s write verifier is\nnot rotated.\n\nA client that receives NFS_UNSTABLE in CB_OFFLOAD follows up with\nCOMMIT to make the copied data durable. With the verifier\nunchanged, COMMIT returns the same value the client just received\nvia CB_OFFLOAD, and the client concludes the copy is durable --\nsilently dropping the data whose writeback in fact failed. This\nviolates the UNSTABLE+COMMIT durability contract (RFC 7862 section\n15.1, RFC 8881 section 18.32) and matches the bug just fixed in\nnfsd_vfs_write() and nfsd_commit().\n\nRotate nn-\u003ewriteverf at the writeback-failure site. The async COPY\nworker has no svc_rqst, so commit_reset_write_verifier() is not\navailable here; calling nfsd_reset_write_verifier() directly\nmirrors the trace-less reset already used by\nnfsd_file_check_write_error() for the same purpose. Filter out\n-EAGAIN and -ESTALE, matching commit_reset_write_verifier(), since\nneither indicates a durable-storage failure."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is in nfsd\u0027s NFSv4.2 async COPY worker (_nfsd_copy_file_range), reached by sending a COMPOUND with OP_COPY (ca_synchronous=false) to the in-kernel NFS server over TCP/2049. No local access to the server is required.\nAC:L - A client can induce the writeback-failure path by filling the export or hitting quota so vfs_fsync_range()/filemap_check_wb_err() returns ENOSPC/EDQUOT after the copy dirties pages, then issue async COPY; CB_OFFLOAD UNSTABLE plus COMMIT with an unchanged verifier is the specified client sequence and needs no race.\nPR:N - Default nfsd deployments use AUTH_SYS/AUTH_NULL with IP-based exports and no cryptographic authentication, so any host allowed by the export can EXCHANGE_ID/CREATE_SESSION, OPEN source and destination files, and issue async COPY by asserting a uid.\nUI:N - The attacking NFS client issues COPY, receives CB_OFFLOAD, and sends COMMIT itself. No administrator or end-user action on the NFS server is required beyond nfsd already serving an NFSv4.2 export.\nS:U - Silent durability failure affects file data on the exported filesystem in the same kernel security authority as nfsd. This is not a VM escape, IOMMU bypass, or sandbox breakout.\nC:N - The defect only skips rotating nn-\u003ewriteverf after a failed COPY fsync; it does not read out-of-bounds, leak kernel memory, or disclose file contents beyond ordinary NFS access.\nI:H - vfs_fsync_range() consumes the writeback error, COMMIT then returns the same verifier, and the client drops the UNSTABLE copy as durable, silently discarding destination file data. Entire COPY ranges, including whole-file copies, can be lost while applications treat them as persisted.\nA:N - The missing verifier rotation does not oops, panic, deadlock, or hang nfsd; the server continues serving RPCs. Impact is incorrect durability reporting and data loss, not loss of the NFS service itself."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:51:19.292Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/cc5f7cef0659a27c13dd33edd8e2f79257b095c6"
        },
        {
          "url": "https://git.kernel.org/stable/c/c6d2f6372c7e0f76b9c148ff7696aec64da0b5b7"
        },
        {
          "url": "https://git.kernel.org/stable/c/8a08ffe73eb2aa6bc6f88763da7e2b55bab6493a"
        },
        {
          "url": "https://git.kernel.org/stable/c/6b13d26cc21b6320a3c61d5e4cee2ce9a589b181"
        },
        {
          "url": "https://git.kernel.org/stable/c/31d4d0a62ec4bafbcdbad142f11ab1f90794b1d0"
        },
        {
          "url": "https://git.kernel.org/stable/c/591134e059e3456180244a826d6917cdc183140b"
        },
        {
          "url": "https://git.kernel.org/stable/c/bf0cd31a9abcb728c17d79b4c2cc533612a8b6af"
        },
        {
          "url": "https://git.kernel.org/stable/c/f5cb2276954cb80987a93ef9f9dfbfdbfc0f10b9"
        }
      ],
      "title": "nfsd: Reset write verifier when async COPY writeback fails",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89706",
    "datePublished": "2026-09-11T19:46:22.561Z",
    "dateReserved": "2026-09-11T19:38:34.751Z",
    "dateUpdated": "2026-10-19T08:51:19.292Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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