# CVE-2026-89706

## Summary

- **CVE ID:** CVE-2026-89706
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: Reset write verifier when async COPY writeback fails

Async COPY captures nn->writeverf at request time and reports it to
the client via CB_OFFLOAD after the worker kthread completes. When
the post-copy vfs_fsync_range() or filemap_check_wb_err() in
_nfsd_copy_file_range() reports an error, the worker correctly
leaves NFSD4_COPY_F_COMMITTED clear so that CB_OFFLOAD encodes
wr_stable_how as NFS_UNSTABLE, but the server's write verifier is
not rotated.

A client that receives NFS_UNSTABLE in CB_OFFLOAD follows up with
COMMIT to make the copied data durable. With the verifier
unchanged, COMMIT returns the same value the client just received
via CB_OFFLOAD, and the client concludes the copy is durable --
silently dropping the data whose writeback in fact failed. This
violates the UNSTABLE+COMMIT durability contract (RFC 7862 section
15.1, RFC 8881 section 18.32) and matches the bug just fixed in
nfsd_vfs_write() and nfsd_commit().

Rotate nn->writeverf at the writeback-failure site. The async COPY
worker has no svc_rqst, so commit_reset_write_verifier() is not
available here; calling nfsd_reset_write_verifier() directly
mirrors the trace-less reset already used by
nfsd_file_check_write_error() for the same purpose. Filter out
-EAGAIN and -ESTALE, matching commit_reset_write_verifier(), since
neither indicates a durable-storage failure.

## Affected Products

- Linux — Linux (eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d)
- Linux — Linux (817c6eb975798647c4bbbfc9eb288aa413ec7f65)
- Linux — Linux (5.10.220)
- Linux — Linux (5.14)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/31d4d0a62ec4bafbcdbad142f11ab1f90794b1d0)
- [CNA](https://git.kernel.org/stable/c/591134e059e3456180244a826d6917cdc183140b)
- [CNA](https://git.kernel.org/stable/c/bf0cd31a9abcb728c17d79b4c2cc533612a8b6af)
- [CNA](https://git.kernel.org/stable/c/f5cb2276954cb80987a93ef9f9dfbfdbfc0f10b9)
- [CNA](https://git.kernel.org/stable/c/cc5f7cef0659a27c13dd33edd8e2f79257b095c6)
- [CNA](https://git.kernel.org/stable/c/c6d2f6372c7e0f76b9c148ff7696aec64da0b5b7)
- [CNA](https://git.kernel.org/stable/c/8a08ffe73eb2aa6bc6f88763da7e2b55bab6493a)
- [CNA](https://git.kernel.org/stable/c/6b13d26cc21b6320a3c61d5e4cee2ce9a589b181)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.51%
- **EPSS Percentile:** 42.4

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