CVE-2026-89706 - Vulnerability Details

- nfsd: Reset write verifier when async COPY writeback fails

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.

Published: 2026-09-11

Score: 7.5 High

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

The flaw causes the NFS daemon to ignore a failed writeback during an asynchronous COPY operation. The verifier used by the server is not rotated when the copy fails, so the client receives a stable‑verifier value and may believe the data is durable after a COMMIT. This violates the NFS durability contract, allowing a client to assume data has been written correctly when it has not, resulting in data loss.

Affected Systems

The vulnerability is present in the Linux versions that contain the unpatched N range is listed, so any kernel lacking the recent patch that restores write‑verifier rotation is susceptible.

Risk and Exploitability

The CVSS score of 7.5 indicates high severity. The EPSS score is less than 1%, showing a very low likelihood of exploitation, and the vulnerability is not listed in the CISA KEV catalog. Based on the description, it is inferred that attackers would need remote network access to send NFS requests to the vulnerable server. The impact is limited to data integrity rather than code execution or disclosure.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`817c6eb975798647c4bbbfc9eb288aa413ec7f65`	affected	< cc5f7cef0659a27c13dd33edd8e2f79257b095c6
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< c6d2f6372c7e0f76b9c148ff7696aec64da0b5b7
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< 8a08ffe73eb2aa6bc6f88763da7e2b55bab6493a
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< 6b13d26cc21b6320a3c61d5e4cee2ce9a589b181
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< 31d4d0a62ec4bafbcdbad142f11ab1f90794b1d0
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< 591134e059e3456180244a826d6917cdc183140b
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< bf0cd31a9abcb728c17d79b4c2cc533612a8b6af
`eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d`	affected	< f5cb2276954cb80987a93ef9f9dfbfdbfc0f10b9
`5.10.220`	affected	< 5.10.270

Linux

affected

Version	Status	Constraints
`5.14`	affected	—
`0`	unaffected	< 5.14
`5.10.270`	unaffected	≤ 5.10.*
`5.15.221`	unaffected	≤ 5.15.*
`6.1.188`	unaffected	≤ 6.1.*
`6.6.157`	unaffected	≤ 6.6.*
`6.12.109`	unaffected	≤ 6.12.*
`6.18.50`	unaffected	≤ 6.18.*
`7.2.4`	unaffected	≤ 7.2.*
`7.3-rc1`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d,31d4d0a62ec4bafbcdbad142f11ab1f90794b1d0)`	affected	code_commit	—
`[eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d,591134e059e3456180244a826d6917cdc183140b)`	affected	code_commit	—
`[eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d,bf0cd31a9abcb728c17d79b4c2cc533612a8b6af)`	affected	code_commit	—
`[eac0b17a77fbd763d305a5eaa4fd1119e5a0fe0d,f5cb2276954cb80987a93ef9f9dfbfdbfc0f10b9)`	affected	code_commit	—
`817c6eb975798647c4bbbfc9eb288aa413ec7f65`	affected	code_commit	—
`[5.10.220,5.11)`	affected	semver	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`5.14`	affected	semver	—
`[0,5.14)`	unaffected	semver	—
`[6.12.109,6.13.0)`	unaffected	semver	—
`[6.18.50,6.19.0)`	unaffected	semver	—
`[7.2.4,7.3.0)`	unaffected	semver	—
`[7.3-rc1,*)`	unaffected	generic	—

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Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Update the Linux kernel to a version that includes the NFS write verifier rotation.
If a distribution update is not available, apply the upstream patch to the kernel.
As a temporary workaround, disable asynchronous copy operations on the NFS serverfs options that turn off async copy) until the patch is applied.

Generated by OpenCVE AI on September 15, 2026 at 19:31 UTC.

Tracking

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Advisories

Source	ID	Title
Debian DSA	DSA-6528-1	linux security update

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00549.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/31d4d0a62ec4bafbcdbad142f11ab1f90794b1d0
https://git.kernel.org/stable/c/591134e059e3456180244a826d6917cdc183140b
https://git.kernel.org/stable/c/6b13d26cc21b6320a3c61d5e4cee2ce9a589b181
https://git.kernel.org/stable/c/8a08ffe73eb2aa6bc6f88763da7e2b55bab6493a
https://git.kernel.org/stable/c/bf0cd31a9abcb728c17d79b4c2cc533612a8b6af
https://git.kernel.org/stable/c/c6d2f6372c7e0f76b9c148ff7696aec64da0b5b7
https://git.kernel.org/stable/c/cc5f7cef0659a27c13dd33edd8e2f79257b095c6
https://git.kernel.org/stable/c/f5cb2276954cb80987a93ef9f9dfbfdbfc0f10b9
https://nvd.nist.gov/vuln/detail/CVE-2026-89706
https://www.cve.org/CVERecord?id=CVE-2026-89706

History

Mon, 14 Sep 2026 12:30:00 +0000

Type	Values Removed	Values Added
References		https://git.kernel.org/stable/c/6b13d26cc21b6320a3c61d5e4cee2ce9a589b181 https://git.kernel.org/stable/c/8a08ffe73eb2aa6bc6f88763da7e2b55bab6493a https://git.kernel.org/stable/c/c6d2f6372c7e0f76b9c148ff7696aec64da0b5b7 https://git.kernel.org/stable/c/cc5f7cef0659a27c13dd33edd8e2f79257b095c6

Sun, 13 Sep 2026 06:45:00 +0000

Type	Values Removed	Values Added
Metrics	cvssV3_1 `{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H'}`	cvssV3_1 `{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}`

Sat, 12 Sep 2026 00:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-367
References		https://nvd.nist.gov/vuln/detail/CVE-2026-89706 https://www.cve.org/CVERecord?id=CVE-2026-89706
Metrics	threat_severity `None`	cvssV3_1 `{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H'}` threat_severity `Important`

Fri, 11 Sep 2026 23:45:00 +0000

Type	Values Removed	Values Added
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.
Title		nfsd: Reset write verifier when async COPY writeback fails
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		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

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-09-11T19:46:22.561Z

Updated: 2026-09-14T12:02:07.475Z

Reserved: 2026-09-11T19:38:34.751Z

Link: CVE-2026-89706

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-09-11T20:19:57.890

Modified: 2026-09-14T13:19:20.523

Link: CVE-2026-89706

Redhat

Severity : Important

Publid Date: 2026-09-11T19:46:22Z

Links: CVE-2026-89706 - Bugzilla

OpenCVE Enrichment

Updated: 2026-09-15T19:45:07Z

Weaknesses

CWE-367
Time-of-check Time-of-use (TOCTOU) Race Condition

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact None

User Interaction None

Subscriptions

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