CVE-2026-90236 NFSD: Release the export reference when reaping open stateids
A reference counting bug in the Linux kernel NFSD module prevents unmounting exports, leading to a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90236?
CVE-2026-90236 is a denial of service vulnerability in Linux, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
NFSD: Release the export reference when reaping open stateids
nfs4_put_stid() releases the svc_export tracked in nfs4_stid.sc_export, but free_ol_stateid_reaplist() frees open and lock stateids by calling ->sc_free() directly, bypassing that path. An open stateid takes an sc_export reference in nfs4_open() and a lock stateid takes its own in init_lock_stateid(); both reach free_ol_stateid_reaplist() through their normal teardown, the open stateid via release_open_stateid() and the lock stateid via nfsd4_release_lockowner(), each through put_ol_stateid_locked(). The reference is therefore never dropped, pinning the export and blocking unmount for the lifetime of the stateid.
Release sc_export in free_ol_stateid_reaplist() the way nfs4_put_stid() does. ->sc_free() runs once per stateid, and a stateid reaches free_ol_stateid_reaplist() or nfs4_put_stid() but never both, so the reference is dropped exactly once. Revoked stateids reach this path with sc_export already cleared by drop_stid_export(), so they are skipped rather than double-freed.
nfs4_put_stid() itself read sc_export before acquiring cl_lock. drop_stid_export() clears that field and releases the reference under cl_lock, so a concurrent revocation could drop the export in the window between the read and the final put, releasing the same reference twice. Read sc_export while cl_lock is held so the two paths serialize and the reference is released exactly once.
Which versions are affected by CVE-2026-90236?
How do I fix CVE-2026-90236?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-90236 being exploited?
There is no known exploitation of CVE-2026-90236 in the wild and no public exploit code.
Sources
Also known as GHSA-frqj-gv5h-9hcc, UBUNTU-CVE-2026-90236.