CVE-2026-89658
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In the Linux kernel, the NFSD module has a use-after-free vulnerability during NFSv4.0 revoked-state cleanup. The nfs40_clean_admin_revoked() function drops the client_lock, and then nfsd4_drop_revoked_stid() uses a client that may have been freed by a concurrent teardown. The lack of client pinning enables a race.
Risk Assessment
An attacker could cause a kernel panic or potentially execute code in kernel context by triggering the race between periodic cleanup and forced client expiration. This affects availability and security of an NFS server.
Recommendation
Update the Linux kernel to a version with the fix that skips expiring clients and pins the client via cl_rpc_users under client_lock. Restrict access to the clients/<id>/ctl file for untrusted users.
Other vulnerabilities in Linux kernel
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup nfs40_clean_admin_revoked() takes a stateid reference under clp->cl_lock, drops nn->client_lock, and calls nfsd4_drop_revoked_stid(), which dereferences the stateid's client through s->sc_client->cl_lock. The stateid reference does not pin the client, so a teardown racing the dropped lock can free the client while nfsd4_drop_revoked_stid() is still using it. This cleanup runs from the laundromat, so a periodic sweep can race force_expire_client() driven by a write to the clients/<id>/ctl file. Skip a client that is already expiring and otherwise pin it with cl_rpc_users under client_lock before dropping the lock, matching nfsd4_revoke_states().