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NVD / CVE Program· CNA Linux

CVE-2026-89704: nfsd: sample writeback error cursor before async COPY loop

Noroxi assessment

Priority: Monitor (action score 30/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.52% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 20a67a7d18221af736f124770c2c5e859b479046, 322422d66d1a04434a0dcc0c9d3a4c4b3f225117, 435e4246c7dfff2fbd76dfdbf91975d5d9f788c9.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 20a67a7d18221af736f124770c2c5e859b479046, 322422d66d1a04434a0dcc0c9d3a4c4b3f225117, 435e4246c7dfff2fbd76dfdbf91975d5d9f788c9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: nfsd: sample writeback error cursor before async COPY loop _nfsd_copy_file_range() samples dst->f_wb_err into "since" after the copy loop, then uses it to detect writeback errors via filemap_check_wb_err() once vfs_fsync_range() returns. Because the nfsd_file cache reuses a single struct file across requests targeting the same inode, a concurrent COMMIT or stable WRITE on dst advances dst->f_wb_err to the current mapping->wb_err via file_check_and_advance_wb_err() during its own vfs_fsync_range(). If that advancement lands between the writeback error appearing in mapping->wb_err and the COPY worker sampling "since", the worker captures the already-advanced cursor, errseq_check() sees cur == since and returns zero, and NFSD4_COPY_F_COMMITTED is set even though writeback failed. CB_OFFLOAD then encodes wr_stable_how = FILE_SYNC4, the client treats the copied data as durable, and the failure becomes silent data loss. Sample since once at the start of the function. The cursor then reflects state in effect before this COPY issues any writes, and filemap_check_wb_err() detects any error that occurs during the copy regardless of which thread first observes it. This matches the pattern used by nfsd_vfs_write() and nfsd4_clone_file_range().

HighCVSS 7.5 · v3.1—No exploit Fix available
Published
Sep 11, 2026
Updated
Oct 19, 2026
EPSS
0.5% · 44th percentile
CWE
—

Report tools

JSON

Action score

30

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CNA vs NVD score

NVD
—
CNA · Linux
7.5
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 5.17affected
    • f14816f2f928c560d28ba344af689f56efcd6f55 and later · before 435e4246c7dfff2fbd76dfdbf91975d5d9f788c9affected · git
    • 3145fe0ebb16e1715ad541a301bc6675c8375fcd and later · before 9f539a1c0791f907eb4e6d04b43178d9962e2defaffected · git
    • 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and later · before 4728504c021656128a07f4693af80ed4a5fcc863affected · git
    • 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and later · before 322422d66d1a04434a0dcc0c9d3a4c4b3f225117affected · git
    • 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and later · before 52b2db7a72e19ac2686fa4b2a52406661e7bf9e2affected · git
    • 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and later · before 8277d4a11ae2cb5495842be558fd946032c24363affected · git
    • 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and later · before a1cbafe756cd5e6ab0e099062f37da7a5b081169affected · git
    • 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and later · before 20a67a7d18221af736f124770c2c5e859b479046affected · git
    • 5.10.124 and later · before 5.10.270affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.190-16.1.190-1
Debian:12linux-6.12before 6.12.111-1~deb12u16.12.111-1~deb12u1
Debian:13linuxbefore 6.12.111-16.12.111-1
Debian:14linuxbefore 7.2.6-17.2.6-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-89702Sep 11, 2026 · nfsd: size fh_verify server sockaddr slot by xpt_locallen
    39Monitor
  • ← EarlierCVE-2026-89703Sep 11, 2026 · nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations
    39Monitor
  • Later →CVE-2026-89705Sep 11, 2026 · nfsd: restore rq_status_counter to even on all nfsd_dispatch() exit paths
    28Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux20a67a7d18221af736f124770c2c5e859b479046Vendor (CNA)
Linux Linux322422d66d1a04434a0dcc0c9d3a4c4b3f225117Vendor (CNA)
Linux Linux435e4246c7dfff2fbd76dfdbf91975d5d9f788c9Vendor (CNA)
Linux Linux4728504c021656128a07f4693af80ed4a5fcc863Vendor (CNA)
Linux Linux5.10.270Vendor (CNA)
Linux Linux5.15.221Vendor (CNA)
Linux Linux52b2db7a72e19ac2686fa4b2a52406661e7bf9e2Vendor (CNA)
Linux Linux8277d4a11ae2cb5495842be558fd946032c24363Vendor (CNA)
Linux Linux9f539a1c0791f907eb4e6d04b43178d9962e2defVendor (CNA)
Linux Linuxa1cbafe756cd5e6ab0e099062f37da7a5b081169Vendor (CNA)
debian:linux6.1.190-1 · Debian:12Package registry (OSV)
debian:linux6.12.111-1 · Debian:13Package registry (OSV)
debian:linux-6.126.12.111-1~deb12u1 · Debian:12Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
high · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
High
Availability impact
None

Weakness class (CWE)

—

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records