Vulnerability-Lookup

FKIE_CVE-2026-89661

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

Severity

Summary

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent post-shutdown use-after-free in unlock_filesystem Writing a filesystem path to /proc/fs/nfsd/unlock_filesystem runs nfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the handler confirms that nn->nfsd_serv is set. Once nfsd has shut down, nfs4_state_destroy_net() has freed nn->conf_id_hashtbl but left the pointer intact, so the cancel helper iterates freed slab memory as an array of struct list_head and then dereferences a bogus nfs4_client when it takes clp->async_lock. A local administrator holding CAP_SYS_ADMIN can reach this use-after-free by stopping the server and then writing to unlock_filesystem; KASAN reports a slab-use-after-free read in nfsd4_cancel_copy_by_sb(). nfsd4_revoke_states() walks the same state tables and for that reason already runs only under nfsd_mutex with nn->nfsd_serv confirmed present. Move the async COPY cancel into that protected section so every NFSv4 state-table walker on this path observes a running server. Async copies exist only while the server runs, so gating the cancel on nn->nfsd_serv loses nothing.

References

	URL	Tags
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/0c1a755b7212e0835398d4df5e782ea85ccd7476
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/292d915d3ba6fd15eeb88351fa10581683073109

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfsctl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "0c1a755b7212e0835398d4df5e782ea85ccd7476",
              "status": "affected",
              "version": "3daab3112f039cf849f96764019b096bb0a39d04",
              "versionType": "git"
            },
            {
              "lessThan": "292d915d3ba6fd15eeb88351fa10581683073109",
              "status": "affected",
              "version": "3daab3112f039cf849f96764019b096bb0a39d04",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfsctl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.0"
            },
            {
              "lessThan": "7.0",
              "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: Prevent post-shutdown use-after-free in unlock_filesystem\n\nWriting a filesystem path to /proc/fs/nfsd/unlock_filesystem runs\nnfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the\nhandler confirms that nn-\u003enfsd_serv is set. Once nfsd has shut down,\nnfs4_state_destroy_net() has freed nn-\u003econf_id_hashtbl but left the\npointer intact, so the cancel helper iterates freed slab memory as an\narray of struct list_head and then dereferences a bogus nfs4_client\nwhen it takes clp-\u003easync_lock. A local administrator holding\nCAP_SYS_ADMIN can reach this use-after-free by stopping the server and\nthen writing to unlock_filesystem; KASAN reports a slab-use-after-free\nread in nfsd4_cancel_copy_by_sb().\n\nnfsd4_revoke_states() walks the same state tables and for that reason\nalready runs only under nfsd_mutex with nn-\u003enfsd_serv confirmed\npresent. Move the async COPY cancel into that protected section so\nevery NFSv4 state-table walker on this path observes a running server.\nAsync copies exist only while the server runs, so gating the cancel on\nnn-\u003enfsd_serv loses nothing."
    }
  ],
  "id": "CVE-2026-89661",
  "lastModified": "2026-09-11T20:19:52.413",
  "metrics": {},
  "published": "2026-09-11T20:19:52.413",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/0c1a755b7212e0835398d4df5e782ea85ccd7476"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/292d915d3ba6fd15eeb88351fa10581683073109"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}

CVE-2026-89661 (GCVE-0-2026-89661)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-11 19:45

Title

NFSD: Prevent post-shutdown use-after-free in unlock_filesystem

Summary

Severity

No CVSS data available.

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/0c1a755b7212e0835…
https://git.kernel.org/stable/c/292d915d3ba6fd15e…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 3daab3112f039cf849f96764019b096bb0a39d04 , < 0c1a755b7212e0835398d4df5e782ea85ccd7476 (git) Affected: 3daab3112f039cf849f96764019b096bb0a39d04 , < 292d915d3ba6fd15eeb88351fa10581683073109 (git)
Linux	Linux	Affected: 7.0 Unaffected: 0 , < 7.0 (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/nfsctl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "0c1a755b7212e0835398d4df5e782ea85ccd7476",
              "status": "affected",
              "version": "3daab3112f039cf849f96764019b096bb0a39d04",
              "versionType": "git"
            },
            {
              "lessThan": "292d915d3ba6fd15eeb88351fa10581683073109",
              "status": "affected",
              "version": "3daab3112f039cf849f96764019b096bb0a39d04",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfsctl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.0"
            },
            {
              "lessThan": "7.0",
              "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": "7.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "7.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Prevent post-shutdown use-after-free in unlock_filesystem\n\nWriting a filesystem path to /proc/fs/nfsd/unlock_filesystem runs\nnfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the\nhandler confirms that nn-\u003enfsd_serv is set. Once nfsd has shut down,\nnfs4_state_destroy_net() has freed nn-\u003econf_id_hashtbl but left the\npointer intact, so the cancel helper iterates freed slab memory as an\narray of struct list_head and then dereferences a bogus nfs4_client\nwhen it takes clp-\u003easync_lock. A local administrator holding\nCAP_SYS_ADMIN can reach this use-after-free by stopping the server and\nthen writing to unlock_filesystem; KASAN reports a slab-use-after-free\nread in nfsd4_cancel_copy_by_sb().\n\nnfsd4_revoke_states() walks the same state tables and for that reason\nalready runs only under nfsd_mutex with nn-\u003enfsd_serv confirmed\npresent. Move the async COPY cancel into that protected section so\nevery NFSv4 state-table walker on this path observes a running server.\nAsync copies exist only while the server runs, so gating the cancel on\nnn-\u003enfsd_serv loses nothing."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-11T19:45:49.086Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/0c1a755b7212e0835398d4df5e782ea85ccd7476"
        },
        {
          "url": "https://git.kernel.org/stable/c/292d915d3ba6fd15eeb88351fa10581683073109"
        }
      ],
      "title": "NFSD: Prevent post-shutdown use-after-free in unlock_filesystem",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89661",
    "datePublished": "2026-09-11T19:45:49.086Z",
    "dateReserved": "2026-09-11T19:38:34.744Z",
    "dateUpdated": "2026-09-11T19:45:49.086Z",
    "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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