CVE-2026-89689
CVE-2026-89689 is a security vulnerability. O3 Security confirms whether CVE-2026-89689 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: don't free session slots that are still in use nfsd4_sequence() can free the very slot it is currently processing. When…
Description
In the Linux kernel, the following vulnerability has been resolved:
nfsd: don't free session slots that are still in use
nfsd4_sequence() can free the very slot it is currently processing. When the session shrinker has reduced se_target_maxslots below se_fchannel.maxreqs, the shrink path checks three conditions before calling free_session_slots():
- se_target_maxslots < maxreqs (shrink was advertised)
- slot->sl_generation == se_slot_gen (slot is up-to-date)
- seq->maxslots <= se_target_maxslots (client acknowledges)
However, seq->slotid is never checked against se_target_maxslots. A client using a slot in the range [se_target_maxslots, maxreqs) can satisfy all three conditions: its slot has the current generation (set by a prior SEQUENCE), and it sends sa_highest_slotid <= se_target_maxslots to acknowledge the reduction.
free_session_slots() then kfrees every slot at index >= se_target_maxslots, including the caller's own slot. The function continues to write sl_seqid, sl_flags, sl_generation, and stores the dangling pointer in cstate->slot. Later, nfsd4_store_cache_entry() copies up to maxresp_cached bytes of the compound reply into the freed sl_data[] array, corrupting whatever slab object now occupies that address.
Additionally, a concurrent thread processing SEQUENCE on a different high-numbered slot can have its slot freed out from under it. NFSD4_SLOT_INUSE is set under nn->client_lock before the lock is released, so any concurrent thread past SEQUENCE will have its slot marked. However, free_session_slots() does not check NFSD4_SLOT_INUSE before freeing.
Fix both problems by:
- Checking that the current request's slotid is below the shrink boundary.
- Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and deferring the shrink if any are active.
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-2026-89689 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-2026-89689 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-2026-89689. 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-2026-89689 in your dependencies?
O3 detects CVE-2026-89689 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.