Vulnerability-Lookup

FKIE_CVE-2026-89678

Vulnerability from fkie_nvd - Published: 2026-09-11 20:19 - Updated: 2026-09-13 07:17

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: fix partial-write detection in nfsd_direct_write nfsd_direct_write() walks a list of write segments and, after each vfs_iocb_iter_write(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset: host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter); if (host_err < 0) return host_err; *cnt += host_err; if (host_err < segments[i].iter.count) break; /* partial write */ vfs_iocb_iter_write() runs the iter through ->write_iter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length: before write_iter: iter.count == original_len after write_iter: iter.count == original_len - host_err The condition then reduces to host_err < original_len - host_err, so the break fires only when less than half of the segment was written. Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->ki_pos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting *cnt to the NFS client. Snapshot the segment's byte count before the write and compare host_err against that snapshot so any short write breaks the loop.

References

	URL	Tags
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/250ec14932d5cfe102f68a57892bb566eee7f83e
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/fa6590dfd16ab55f03b658b079072ace3504825e

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/vfs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "fa6590dfd16ab55f03b658b079072ace3504825e",
              "status": "affected",
              "version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
              "versionType": "git"
            },
            {
              "lessThan": "250ec14932d5cfe102f68a57892bb566eee7f83e",
              "status": "affected",
              "version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/vfs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix partial-write detection in nfsd_direct_write\n\nnfsd_direct_write() walks a list of write segments and, after each\nvfs_iocb_iter_write(), tries to detect a short write so the loop can\nstop before placing the next segment at a wrong file offset:\n\n    host_err = vfs_iocb_iter_write(file, kiocb, \u0026segments[i].iter);\n    if (host_err \u003c 0)\n            return host_err;\n    *cnt += host_err;\n    if (host_err \u003c segments[i].iter.count)\n            break;\t/* partial write */\n\nvfs_iocb_iter_write() runs the iter through -\u003ewrite_iter(), which\nadvances the iter by the number of bytes written. By the time the\ncheck runs, segments[i].iter.count is the residual, not the original\nrequest length:\n\n    before write_iter: iter.count == original_len\n    after  write_iter: iter.count == original_len - host_err\n\nThe condition then reduces to host_err \u003c original_len - host_err, so\nthe break fires only when less than half of the segment was written.\nAny short write completing between 50% and 99% of the segment slips\nthrough; the loop advances to the next segment with kiocb-\u003eki_pos\nonly bumped by the short amount, writing the next segment\u0027s payload\nat the wrong offset and over-reporting *cnt to the NFS client.\n\nSnapshot the segment\u0027s byte count before the write and compare\nhost_err against that snapshot so any short write breaks the loop."
    }
  ],
  "id": "CVE-2026-89678",
  "lastModified": "2026-09-13T07:17:33.533",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-09-11T20:19:54.523",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/250ec14932d5cfe102f68a57892bb566eee7f83e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fa6590dfd16ab55f03b658b079072ace3504825e"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}

CVE-2026-89678 (GCVE-0-2026-89678)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33

Title

nfsd: fix partial-write detection in nfsd_direct_write

Summary

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/fa6590dfd16ab55f0…
https://git.kernel.org/stable/c/250ec14932d5cfe10…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 06c5c97293e3fca99ce15da157068edf45a7c6e4 , < fa6590dfd16ab55f03b658b079072ace3504825e (git) Affected: 06c5c97293e3fca99ce15da157068edf45a7c6e4 , < 250ec14932d5cfe102f68a57892bb566eee7f83e (git)
Linux	Linux	Affected: 6.19 Unaffected: 0 , < 6.19 (semver) Unaffected: 7.2.4 , ≤ 7.2.* (semver) Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/vfs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "fa6590dfd16ab55f03b658b079072ace3504825e",
              "status": "affected",
              "version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
              "versionType": "git"
            },
            {
              "lessThan": "250ec14932d5cfe102f68a57892bb566eee7f83e",
              "status": "affected",
              "version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/vfs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix partial-write detection in nfsd_direct_write\n\nnfsd_direct_write() walks a list of write segments and, after each\nvfs_iocb_iter_write(), tries to detect a short write so the loop can\nstop before placing the next segment at a wrong file offset:\n\n    host_err = vfs_iocb_iter_write(file, kiocb, \u0026segments[i].iter);\n    if (host_err \u003c 0)\n            return host_err;\n    *cnt += host_err;\n    if (host_err \u003c segments[i].iter.count)\n            break;\t/* partial write */\n\nvfs_iocb_iter_write() runs the iter through -\u003ewrite_iter(), which\nadvances the iter by the number of bytes written. By the time the\ncheck runs, segments[i].iter.count is the residual, not the original\nrequest length:\n\n    before write_iter: iter.count == original_len\n    after  write_iter: iter.count == original_len - host_err\n\nThe condition then reduces to host_err \u003c original_len - host_err, so\nthe break fires only when less than half of the segment was written.\nAny short write completing between 50% and 99% of the segment slips\nthrough; the loop advances to the next segment with kiocb-\u003eki_pos\nonly bumped by the short amount, writing the next segment\u0027s payload\nat the wrong offset and over-reporting *cnt to the NFS client.\n\nSnapshot the segment\u0027s byte count before the write and compare\nhost_err against that snapshot so any short write breaks the loop."
        }
      ],
      "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 - nfsd_direct_write() is reached from NFSv2/v3 WRITE (nfsd_proc_write/nfsd3_proc_write) and NFSv4 WRITE (nfsd4_write) in the in-kernel NFS server via svc_recv/svc_process over TCP/UDP 2049, so a remote client supplies the payload, offset, and length on the wire.\nAC:L - On nfsd hosts with io_cache_write=DIRECT, the attacker chooses WRITE offset and size to force a prefix/middle/suffix split (nsegs\u003e=2) and can induce a 50-99% short write via quota, ENOSPC, or a concurrent truncate they also send; no race or layout outside their control is required.\nPR:N - Typical nfsd deployments accept AUTH_SYS/AUTH_NULL with IP-based export ACLs, so a network peer can MOUNT/LOOKUP, spoof an owner UID, and issue WRITE without cryptographic authentication or a local account on the NFS server.\nUI:N - The attacking NFS client sends the WRITE RPC itself; no separate victim user or administrator action on the server is required at attack time beyond nfsd already exporting a writable filesystem with direct writes enabled.\nS:U - Misplaced writes and the over-reported WRITE count affect only file data on the host running nfsd, remaining in that kernel/filesystem security authority without crossing a VM, IOMMU, or sandbox boundary.\nC:N - The bug only writes the client\u0027s own payload at a shifted file offset and over-reports the WRITE byte count; it does not read kernel memory or other inodes and is not a use-after-free or out-of-bounds read.\nI:H - After a 50-99% short write the loop continues and places the next segment at ki_pos advanced only by the short count, silently storing payload at the wrong file offset and over-reporting *cnt so clients treat corrupted server data as fully committed; when uncertain versus Low, High is required.\nA:N - The defect corrupts file contents and the NFS WRITE count without oops, panic, BUG_ON, deadlock, or hang; files remain accessible and nfsd workers continue, so there is no kernel or service crash."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-13T06:33:01.153Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/fa6590dfd16ab55f03b658b079072ace3504825e"
        },
        {
          "url": "https://git.kernel.org/stable/c/250ec14932d5cfe102f68a57892bb566eee7f83e"
        }
      ],
      "title": "nfsd: fix partial-write detection in nfsd_direct_write",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89678",
    "datePublished": "2026-09-11T19:46:02.184Z",
    "dateReserved": "2026-09-11T19:38:34.747Z",
    "dateUpdated": "2026-09-13T06:33:01.153Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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