CVE-2026-89676 nfsd: fix stale s2s_cp_stateids IDR entry for async COPY
A use-after-free vulnerability in the Linux kernel NFS server allows attackers to cause denial of service or execute arbitrary code via async COPY operations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89676?
CVE-2026-89676 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: fix stale s2s_cp_stateids IDR entry for async COPY
For an async COPY, nfsd4_copy() called nfs4_init_copy_state() before dup_copy_fields(), so the s2s_cp_stateids IDR was pointed at &u->copy->cp_stateid -- memory in the per-rqstp COMPOUND buffer that is reused by the next request. dup_copy_fields() copies only the value into async_copy, so the IDR slot dangled at the transient buffer for the whole background copy. Any IDR walker then dereferences reused request memory: the laundromat reads cs_type from it and, if the bytes look like an expired NFS4_COPYNOTIFY_STID, follows into refcount_dec()/idr_remove()/kfree() on garbage; manage_cpntf_state() has the same exposure via idr_find().
Duplicate the fields first, then register the stateid on the stable async_copy. result->cb_stateid is unchanged.
Which versions are affected by CVE-2026-89676?
How do I fix CVE-2026-89676?
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-2026-89676 being exploited?
There is no known exploitation of CVE-2026-89676 in the wild and no public exploit code.
Sources
Also known as AZL-100704, BELL-CVE-2026-89676, DEBIAN-CVE-2026-89676, GHSA-gwc7-hc26-hx5g, UBUNTU-CVE-2026-89676.