CVE-2026-89664 nfsd: release OPEN-decoded posix ACLs via op_release
A memory leak in the Linux kernel NFS server allows attackers to exhaust kernel memory via malformed OPEN compounds, causing 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-2026-89664?
CVE-2026-89664 is a high-severity memory corruption 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: release OPEN-decoded posix ACLs via op_release
nfsd4_decode_createhow4() calls nfsd4_decode_fattr4(), which allocates refcounted struct posix_acl objects via posix_acl_alloc() and stores them in open->op_pacl and open->op_dpacl. These pointers must be released once the OPEN compound finishes.
When nfsd4_decode_open_claim4() returns a non-seqid-mutating error, the dispatcher short-circuits before op_func runs:
nfsd4_proc_compound() if (op->status && op->opnum == OP_OPEN) op->status = nfsd4_open_omfg(...) if (!seqid_mutating_err(ntohl(op->status))) return op->status; /* nfsd4_open() never runs */ ... opdesc->op_release(&op->u) /* must still release op_pacl/op_dpacl */
Before this change OP_OPEN had no .op_release in nfsd4_ops[], and the release pair lived inside nfsd4_open() at its out_err: label. On the short-circuit path nfsd4_open() is never invoked, so both posix_acl refs leak on every malformed OPEN compound that carries valid POSIX ACL createhow4 attributes.
Add nfsd4_open_release() and wire it as .op_release for OP_OPEN. posix_acl_release() is NULL-safe, so the single release site covers both the normal path and the nfsd4_open_omfg short-circuit. Remove the matching posix_acl_release() pair from nfsd4_open()'s out_err: label to avoid double-releasing.
The compound loop has two encoding branches: nfsd4_encode_operation() for normal ops, and nfsd4_encode_replay() for v4.0 replayed ops. op_release was only called from nfsd4_encode_operation(), so resources attached to op->u leak on the replay path.
Move the op_release() call out of nfsd4_encode_operation() and the replay branch, placing it after the if-else in nfsd4_proc_compound(). This gives a single call site in a fairly obviously-correct place, covering both the normal encoding and replay paths.
Which versions are affected by CVE-2026-89664?
How do I fix CVE-2026-89664?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89664 being exploited?
There is no known exploitation of CVE-2026-89664 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-89664, GHSA-2mmp-54r9-hmh2, UBUNTU-CVE-2026-89664.