CVE-2026-89662: Red Hat Prevent lock owner use-after-free during client teardown
This Red Hat advisory covers CVE-2026-89662 in Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6 and Red Hat Enterprise Linux 7.
Key facts
- Vendor rating
- High, CVSS 7
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H· base score 9.8, scored by LinuxAttack vector: network. Attack complexity: low. Privileges required: none. User interaction: none. Scope: unchanged. Confidentiality impact: high. Integrity impact: high. Availability impact: high.- EPSS
- 0.69% chance of exploitation in the next 30 days (53rd percentile). FIRST EPSS, .
- CISA SSVC
- Exploitation: none observed. Automatable: yes. Technical impact: total. CISA, .
- CISA KEV
- Not listed (catalogue checked )
- Source published
- Source revised
- Listed by VulniPulse
Compiled by VulniPulse from the linked sources. How records are collected and checked.
Affected products & platforms
Description
In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent lock owner use-after-free during client teardown __destroy_client() releases a client's open owners, but a lock owner whose only reference is a blocked lock (nbl) stays on cl_ownerstr_hashtbl. client_has_state() does not count a bare owner, so DESTROY_CLIENTID can reach __destroy_client() with such owners present. __destroy_client() then walks the table, calling remove_blocked_locks() on each owner without a reference.
Freeing a blocked lock drops the owner reference held via flc_owner. The per-net laundromat reaps blocked locks from nn->blocked_locks_lru independently of client state.
The two paths share blocked_locks_lock only for the list splice, not the owner's lifetime. The laundromat therefore frees the owner as __destroy_client() dereferences it, a NULL dereference in remove_blocked_locks(). nfsd4_release_lockowner() holds a reference across the same call; __destroy_client() does not.
Hold cl_lock across the walk, taking a reference and unhashing each owner, then drop it before remove_blocked_locks() and nfs4_put_stateowner(), which take blocked_locks_lock and cl_lock. A flaw was found in the Linux kernel's Network File System Daemon (NFSD).
Text from the source record.
CVE-2026-89662 in other vendors' advisories
- NetApp: NTAP-20261002-0013, critical severity
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