CVE-2026-89663
CVE-2026-89663 is a security vulnerability. O3 Security confirms whether CVE-2026-89663 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
In the Linux kernel, the following vulnerability has been resolved: nfsd: revoke copy-notify stateids before dropping their reference Copy-notify stateids live in the s2s_cp_stateids…
Description
In the Linux kernel, the following vulnerability has been resolved:
nfsd: revoke copy-notify stateids before dropping their reference
Copy-notify stateids live in the s2s_cp_stateids IDR and on their parent stid's sc_cp_list, pinned by a single membership reference. _free_cpntf_state_locked() only unlinks an entry once its refcount reaches zero, so any revoke path that runs while a concurrent find_cpntf_state()/manage_cpntf_state() holder has elevated cs_count drops the reference without unlinking, leaving the entry discoverable with its membership reference already consumed. A second revoke or a laundromat tick then frees it while the reader still holds the pointer -- a KASAN-detectable use-after-free at the reader's nfs4_put_cpntf_state().
This affected all three revoke paths:
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The parent-stid drain (nfs4_free_cpntf_statelist()) repeatedly called _free_cpntf_state_locked() on the first list entry; a holder that had bumped cs_count made it return early, so the next iteration re-decremented and burned the holder's reference.
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OFFLOAD_CANCEL (manage_cpntf_state()) and laundromat expiry likewise used _free_cpntf_state_locked() and could drop 2->1 without unlinking.
Add revoke_cpntf_state_locked(), which unhashes the entry from the IDR and sc_cp_list first (deferring the final free to any holder), and use it from all three revoke paths. The drain now walks with list_for_each_entry_safe() and revokes each entry unconditionally, so it terminates in one pass per entry regardless of cs_count. The unhash is gated on !list_empty(&cps->cp_list); the idr_remove() gate matters because idr_alloc_cyclic() may have recycled the so_id by then. Keep _free_cpntf_state_locked() for the reference-holder put path only, where a concurrent revoke may already have unlinked the entry (its list_del_init() then a no-op).
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of the affected component has shipped for CVE-2026-89663 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-89663 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-89663. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-89663 in your dependencies?
O3 detects CVE-2026-89663 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.