# CVE-2026-89664

## Summary

- **CVE ID:** CVE-2026-89664
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## 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.

## Affected Products

- Linux — Linux (5fc51dfc2eb160bd7ab3251ab1767cacf9c8bf05)
- Linux — Linux (7.0)
- Linux — Linux (0)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/5b3a7d7c23c071efe12dd1bc1d2e5f97c4892921)
- [CNA](https://git.kernel.org/stable/c/8215892993ea9f5231da4fa9eb42428a286fce8b)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.49%
- **EPSS Percentile:** 40.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._