How severe is CVE-2026-90036?

CVE-2026-90036 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-90036?

CVE-2026-90036 affects the following packages: Kernel (Linux). Ecosystems affected: Linux.

How do I fix CVE-2026-90036?

Update Kernel to 6.18.51 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-90036 is resolved across your whole dependency graph.

How do I detect CVE-2026-90036 in my Linux dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. 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.

How do I mitigate CVE-2026-90036 if there is no patch (or I can't update yet)?

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 does O3 Security protect against CVE-2026-90036?

O3 pinpoints whether CVE-2026-90036 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-90036 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-90036 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was CVE-2026-90036 published, and has it been updated?

CVE-2026-90036 was published on September 16, 2026 and was last updated on September 17, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐧

🐧 Linux

Not in CISA KEV

CRITICAL severity

CVE-2026-90036

CRITICAL

CVE-2026-90036 is a critical-severity (CVSS 9.8) vulnerability in Kernel. O3 Security confirms whether CVE-2026-90036 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

NFSD: Prevent client use-after-free during blocked-lock reaping

Published

Sep 16, 2026

Updated

Sep 17, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 17, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

🐧Kernel

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.

Description

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Prevent client use-after-free during blocked-lock reaping

A bare lock owner -- its only remaining reference a blocked lock on nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but no reference keeping the client alive. When the per-net laundromat reaps such a lock, freeing the nbl drops the owner reference held through flc_owner, and the final nfs4_put_stateowner() takes the client's cl_lock. Because the laundromat detaches the nbl first, __destroy_client() no longer finds it, so a concurrent force_expire_client() can free the client before nfs4_put_stateowner() runs, dereferencing cl_lock in freed memory.

Pin the client with cl_rpc_users before dropping nn->blocked_locks_lock, and skip clients already expiring, whose blocked locks __destroy_client() frees while holding an owner reference. Take nn->client_lock outside nn->blocked_locks_lock. Every other site holds nn->blocked_locks_lock as a leaf, acquiring no further lock, so placing nn->client_lock outside it cannot form a lock-order cycle.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐧Linux	`Kernel`	≥ 4.9.0&&< 6.18.51	6.18.51

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. 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.
Fix
Update Kernel to 6.18.51 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-90036 is resolved across your whole dependency graph.
Workarounds
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-2026-90036 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-2026-90036. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during blocked-lock reaping A bare lock owner -- its only remaining reference a blocked lock on nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but no reference keeping the client alive. When the per-net laundromat reaps such a lock, freeing the nbl drops the owner reference held through flc_owner, and the final nfs4_put_stateowner() takes the client's cl_lock. Because the laundromat detaches the nbl first, __destroy_client() no longer finds it, so a concurrent force_expire

O3 Security · Impact-Aware SCA

Is CVE-2026-90036 in your dependencies?

O3 detects CVE-2026-90036 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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