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CVE-2026-89631VulnerabilityPublished Updated

Microsoft · smb: client: reject a tree connect response whose byte count is too small

Affects MicrosoftSource GCVE Database

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Authoritative record:CVE-2026-89631· Critical 9.1

Not known to be exploited · CVSS 9.1 Critical · fixed in d837645a719151ed392d4d9cab4571c2753dab12 : patch Microsoft as a priority.

Data as of 7 Nov 2026, 12:19 UTC

CVSS 3.1 base score
9.1Critical
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (Linux)CVSS 3.19.1
Patch
Available – fixed in d837645a719151ed392d4d9cab4571c2753dab12, bb99866cb1d3d5e8201200a8692fd8da3106a8fd, 411e484fe71a7f1028de617447edad9cb6d9d68a +3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 11 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 7 Nov 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ cc20c031bb067eb3280a1c4b5c42295093e24863, < d837645a719151ed392d4d9cab4571c2753dab12
Fixed in
  • d837645a719151ed392d4d9cab4571c2753dab12
LinuxLinuxAffected
  • ≥ cc20c031bb067eb3280a1c4b5c42295093e24863, < bb99866cb1d3d5e8201200a8692fd8da3106a8fd
Fixed in
  • bb99866cb1d3d5e8201200a8692fd8da3106a8fd
LinuxLinuxAffected
  • ≥ cc20c031bb067eb3280a1c4b5c42295093e24863, < 411e484fe71a7f1028de617447edad9cb6d9d68a
Fixed in
  • 411e484fe71a7f1028de617447edad9cb6d9d68a
LinuxLinuxAffected
  • ≥ cc20c031bb067eb3280a1c4b5c42295093e24863, < 65deb18359341141d37dc86fc7853511be3c87a7
Fixed in
  • 65deb18359341141d37dc86fc7853511be3c87a7
LinuxLinuxAffected
  • ≥ cc20c031bb067eb3280a1c4b5c42295093e24863, < 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d
Fixed in
  • 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d
LinuxLinuxAffected
  • ≥ cc20c031bb067eb3280a1c4b5c42295093e24863, < 2ae219762ebac929bf6ab3473681f10ed566af08
Fixed in
  • 2ae219762ebac929bf6ab3473681f10ed566af08

Description

To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

References

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