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CVE-2026-89692 (GCVE-0-2026-89692)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33
VLAI
Title
nfsd: clear CALLBACK_RUNNING on failed delegation recall queue
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: clear CALLBACK_RUNNING on failed delegation recall queue nfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit at entry to serialize recall work, then calls nfsd4_run_cb() to queue the recall. When the queue attempt fails the refcount bump is undone, but the RUNNING bit is left set. The only site that clears the bit is nfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the workqueue and is therefore unreachable when nothing was queued. The bit becomes a permanent latch on dp->dl_recall.cb_flags: every subsequent break_lease() on the same delegation hits the early-return guard in nfsd_break_one_deleg() and silently skips the recall, so the delegation is never broken and the conflicting open or lock stalls. Fix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside the refcount_dec.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1054e8ffc5c492f341bdf1888b882f1d163dd3d8 , < b137930ee52e3ef38915a3511d4c070463b63a32 (git)
Affected: 1054e8ffc5c492f341bdf1888b882f1d163dd3d8 , < cb2d0c4d1b3d301d042ed61365eaa8cb0141a254 (git)
Affected: 1054e8ffc5c492f341bdf1888b882f1d163dd3d8 , < b036727d334b1b7cd4c1f1fba3b59ba93a6bbe96 (git)
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Linux Linux Affected: 6.15
Unaffected: 0 , < 6.15 (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4state.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: clear CALLBACK_RUNNING on failed delegation recall queue\n\nnfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit\nat entry to serialize recall work, then calls nfsd4_run_cb() to queue\nthe recall.  When the queue attempt fails the refcount bump is undone,\nbut the RUNNING bit is left set.  The only site that clears the bit is\nnfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the\nworkqueue and is therefore unreachable when nothing was queued.\n\nThe bit becomes a permanent latch on dp-\u003edl_recall.cb_flags: every\nsubsequent break_lease() on the same delegation hits the early-return\nguard in nfsd_break_one_deleg() and silently skips the recall, so the\ndelegation is never broken and the conflicting open or lock stalls.\n\nFix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside\nthe refcount_dec."
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            "baseSeverity": "HIGH",
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              "value": "AV:N - nfsd_break_one_deleg() runs in in-kernel nfsd (fs/nfsd/nfs4state.c) and is reached over TCP/2049 via svc_process to nfsd_dispatch to nfsd4_proc_compound: a remote NFSv4 OPEN grants a delegation, then a conflicting OPEN hits nfsd_file_acquire/nfsd_open_break_lease to __break_lease to nfsd_break_deleg_cb().\nAC:L - The attacker drives both sides with two NFSv4 clients: one holds the delegation while the other sends conflicting OPEN/LOCK/SETATTR to invoke nfsd_break_one_deleg(), and can DESTROY_CLIENTID or flap the backchannel so queue_work() fails; the sequence is retryable and needs no uninfluenced memory layout.\nPR:N - Default AUTH_SYS/AUTH_NULL nfsd exports do not cryptographically verify RPC credentials; any host allowed by the export can EXCHANGE_ID/SETCLIENTID, OPEN to receive a delegation, and issue a conflicting OPEN with no local Linux account or capability.\nUI:N - The attacking NFS clients send the OPEN, conflicting OPEN, and optional DESTROY_CLIENTID RPCs themselves; no victim user on the NFS server must mount a filesystem, open a file, or otherwise interact at attack time.\nS:U - The latched NFSD4_CALLBACK_RUNNING bit and stalled lease-break live in kernel nfsd/VFS state on the NFS server; this is not a VM, IOMMU, or sandbox boundary crossing.\nC:N - The bug only leaves NFSD4_CALLBACK_RUNNING set so later recalls are skipped; it does not read attacker-inaccessible kernel memory, leak pointers, or return extra data to the client.\nI:N - There is no use-after-free, out-of-bounds write, or other memory corruption, and conflicting writers are blocked rather than committing unauthorized file changes, so integrity is unaffected.\nA:H - When nfsd4_run_cb() fails, RUNNING stays set, later break_lease() skips CB_RECALL, nfsd4_cb_recall_prepare never queues the delegation on del_recall_lru, and fl_break_time is zeroed so VFS will not expire the lease; conflicting opens/locks then stall or retry NFS4ERR_JUKEBOX indefinitely, denying the file and NFS service."
            }
          ]
        }
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        "dateUpdated": "2026-09-13T06:33:17.329Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "cveId": "CVE-2026-89692",
    "datePublished": "2026-09-11T19:46:12.040Z",
    "dateReserved": "2026-09-11T19:38:34.749Z",
    "dateUpdated": "2026-09-13T06:33:17.329Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
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      "current_release_date": "2026-09-15T14:05:57+00:00",
      "cve": "CVE-2026-89692",
      "id": "CVE-2026-89692",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "91",
      "product_status:known_not_affected": "185",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: nfsd: clear CALLBACK_RUNNING on failed delegation recall queue",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89692.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-16T00:00:07Z",
      "cve": "CVE-2026-89692",
      "id": "CVE-2026-89692",
      "initial_release_date": "2026-09-12T16:23:38Z",
      "product_status:known_not_affected": "353",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89692",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89692.json",
      "version": "6"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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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.