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NVD / CVE Program· CNA Linux

CVE-2026-89631: smb: client: reject a tree connect response whose byte count is too small

Noroxi assessment

Priority: Monitor (action score 36/100)

  • 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: 0.49% (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.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: Linux Linux 2ae219762ebac929bf6ab3473681f10ed566af08, 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d, 411e484fe71a7f1028de617447edad9cb6d9d68a; azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 Release Notes; azl3 kernel 6.6.159.1-1 on Azure Linux 3.0 Release Notes.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 2ae219762ebac929bf6ab3473681f10ed566af08, 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d, 411e484fe71a7f1028de617447edad9cb6d9d68a; azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 Release Notes; azl3 kernel 6.6.159.1-1 on Azure Linux 3.0 Release Notes 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: smb: client: reject a tree connect response whose byte count is too small CIFSTCon() bounds its strnlen() over the byte area with the server's ByteCount minus two, which for ByteCount 0 or 1 goes negative as an int and converts to a huge size_t. The later subtraction wraps the __u16 bytes_left, and that is what bounds cifs_strndup_from_utf16(): a bound of up to 65535 against a ~16 KB cifs_req_poolp object runs off the end of the slab object, and the bytes reach userspace through tcon->nativeFileSystem in /proc/fs/cifs/DebugData. Reject a byte area too small for what the parser consumes. Two bytes is the least it can consume, and no conformant response carries fewer. The new trace point is the 129th smb_eio_trace entry, which __mode(byte) cannot represent, so the attribute goes with it.

CriticalCVSS 9.1 · v3.1—No exploit Fix available
Published
Sep 11, 2026
Updated
Oct 30, 2026
EPSS
0.4% · 42th percentile
CWE
—

Report tools

JSON

Action score

36

Monitor

Low priority for now.

CVSS
36 / 40 · 9.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
9.1
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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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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  • when EPSS rises 20 points in a week

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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

    • 2.6.30affected
    • cc20c031bb067eb3280a1c4b5c42295093e24863 and later · before bb99866cb1d3d5e8201200a8692fd8da3106a8fdaffected · git
    • cc20c031bb067eb3280a1c4b5c42295093e24863 and later · before d837645a719151ed392d4d9cab4571c2753dab12affected · git
    • cc20c031bb067eb3280a1c4b5c42295093e24863 and later · before 2ae219762ebac929bf6ab3473681f10ed566af08affected · git
    • cc20c031bb067eb3280a1c4b5c42295093e24863 and later · before 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2daffected · git
    • cc20c031bb067eb3280a1c4b5c42295093e24863 and later · before 411e484fe71a7f1028de617447edad9cb6d9d68aaffected · git
    • cc20c031bb067eb3280a1c4b5c42295093e24863 and later · before 65deb18359341141d37dc86fc7853511be3c87a7affected · git
    • before 2.6.30not affected · semver
    • 6.1.191 and later · up to and including 6.1.*not affected · semver
    • 6.6.160 and later · up to and including 6.6.*not affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
AlmaLinux:10kernelbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64kbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debugbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debug-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debug-develbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debug-devel-matchedbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debug-modulesbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debug-modules-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-debug-modules-extrabefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-develbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-devel-matchedbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-modulesbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-modules-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-64k-modules-extrabefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-abi-stablelistsbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-cross-headersbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-debugbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-debug-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-debug-develbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-debug-devel-matchedbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-debug-modulesbefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2
AlmaLinux:10kernel-debug-modules-corebefore 6.12.0-211.67.1.el10_26.12.0-211.67.1.el10_2

+96

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-2026-89629Sep 11, 2026 · HID: corsair-void: Check size of status and firmware events before reading them
    0Monitor
  • ← EarlierCVE-2026-89630Sep 11, 2026 · smb: client: restore the data_offset bound in is_valid_oplock_break()
    36Monitor
  • Later →CVE-2026-89632Sep 11, 2026 · smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()
    32Monitor

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 Linux2ae219762ebac929bf6ab3473681f10ed566af08Vendor (CNA)
Linux Linux3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2dVendor (CNA)
Linux Linux411e484fe71a7f1028de617447edad9cb6d9d68aVendor (CNA)
Linux Linux65deb18359341141d37dc86fc7853511be3c87a7Vendor (CNA)
Linux Linuxbb99866cb1d3d5e8201200a8692fd8da3106a8fdVendor (CNA)
Linux Linuxd837645a719151ed392d4d9cab4571c2753dab12Vendor (CNA)
azl3 kernel 6.6.150.1-1 on Azure Linux 3.0—Microsoft (MSRC)
azl3 kernel 6.6.152.1-1 on Azure Linux 3.0—Microsoft (MSRC)
azl3 kernel 6.6.157.1-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
azl3 kernel 6.6.159.1-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
almalinux:bpftool4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-core6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug-core6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug-devel6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug-devel-matched6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug-modules6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug-modules-core6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-debug-modules-extra6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-devel6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-64k-devel-matched6.12.0-211.67.1.el10_2 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-abi-stablelists4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-core4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-cross-headers4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug-core4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug-devel4.18.0-553.176.1.el8_10 · AlmaLinux:8Package registry (OSV)

+20

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
high · data can be read
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
None
Availability impact
High

Weakness class (CWE)

—

CVSS vector

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

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. SSVC exploitation— → none
  2. Fix✗ → ✓

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

References

Show all references (5 more)

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

All records