CVE-2026-89669 nfsd: initialize copy-notify stateid before publishing it
A race condition in the Linux kernel NFS server allows attackers to trigger a use-after-free via crafted OFFLOAD_CANCEL requests, potentially leading to code execution or crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89669?
CVE-2026-89669 is a critical use after free vulnerability in Linux, published on 11 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: initialize copy-notify stateid before publishing it
nfsd4_copy_notify() finished initializing the cpntf state after nfs4_alloc_init_cpntf_state() had already linked it into the s2s_cp_stateids IDR and the parent's sc_cp_list, with cs_count == 1 (the membership reference) and none held for the caller. A racing OFFLOAD_CANCEL (crafted cl_id == nn->s2s_cp_cl_id plus the guessable so_id) could reach manage_cpntf_state() and free the entry, turning the caller's subsequent cpn_cnr_stateid read and cp_p_stateid/cp_p_clid writes into use-after-free. The owning clientid was also only recorded after publication, so it could not gate an ownership check in that window.
Record cp_p_stateid and cp_p_clid inside nfs4_alloc_init_cpntf_state() before nfs4_init_cp_state() publishes the entry, and return it with an extra reference. The caller reads the stateid under that reference and drops it with nfs4_put_cpntf_state(); on a late error the laundromat reaps the entry.
Which versions are affected by CVE-2026-89669?
How do I fix CVE-2026-89669?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-89669 being exploited?
There is no known exploitation of CVE-2026-89669 in the wild and no public exploit code.
Sources
Also known as AZL-100076, BELL-CVE-2026-89669, DEBIAN-CVE-2026-89669, GHSA-76rg-3h22-jw6r, UBUNTU-CVE-2026-89669.