EUVD-2026-76604
GHSA-mcqc-fm6v-5h2r
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Requires authenticated NFSv4 session for delegation issuance (PR:L) and a non-trivial queue failure condition (AC:H); no confidentiality or integrity impact.
Primary rating from Vendor (Linux).
CVSS VectorVendor: Linux
Lifecycle Timeline
5DescriptionCVE.org
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.
AnalysisAI
Delegation recall permanently stalls in Linux kernel NFSD when the callback queue fails during a lease break. In nfsd_break_one_deleg(), the NFSD4_CALLBACK_RUNNING bit is set atomically to serialize recall work, but if nfsd4_run_cb() cannot queue the workitem, the refcount is decremented while the bit is left set - creating a permanent latch that causes every subsequent break_lease() on the same delegation to silently return early. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The following conditions must all hold simultaneously: (1) The Linux kernel is running as an NFSv4 or NFSv4.1 NFS server with the NFSD subsystem active (nfsd loaded, exports configured). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The input CVSS vector AV:N/AC:L/PR:N/UI:N (score 7.5) is overstated for this vulnerability. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to a patched kernel release: Linux 6.18.50, 7.2.4, or 7.3-rc1 include the fix (one-line clear of NFSD4_CALLBACK_RUNNING on the !queued branch in nfsd_break_one_deleg()). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all Linux-based NFS servers in your infrastructure and document their current kernel versions and vendor. …
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