Skip to content
Fencer Vulns
critical 9.1

CVE-2026-89631 in the critical feed json

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

published 2026-09-11 58 d ago modified 2026-10-30 9 d ago also EUVD-2026-76543

cvss
9.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 6.1.191, 6.6.160, 6.12.114, 6.18.51, 7.2.4, 7.3
  • linux Debian 13 6.12.115-2
  • linux Debian 14 7.2.6-1

debian advisories DEBIAN-CVE-2026-89631

  • linux Ubuntu 26.04 LTS 7.0.0-42.42
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1016.17
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1016.18
  • linux-ibm Ubuntu 26.04 LTS 7.0.0-1017.17
  • linux-riscv Ubuntu 26.04 LTS 7.0.0-42.42.1
  • linux-oracle Ubuntu 26.04 LTS 7.0.0-1015.16
  • linux-hwe-7.0 Ubuntu 24.04 LTS 7.0.0-42.42~24.04.1
  • linux-oem-7.0 Ubuntu 26.04 LTS 7.0.0-1017.17

ubuntu advisories UBUNTU-CVE-2026-89631

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 8 4.18.0-553.176.1.el8_10
  • perf RHEL 8 4.18.0-553.176.1.el8_10
  • bpftool RHEL 8 4.18.0-553.176.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.176.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.176.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.176.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.176.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.176.1.el8_10

red hat advisories RHSA-2026:85773RHSA-2026:85774RHSA-2026:85321

  • kernel-rt Linux Micro 6.2 6.12.0-160000.40.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.40.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.40.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.40.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.40.1.160000.2.29
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.40.1
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.40.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.40.1

suse advisories SUSE-SU-2026:5121-1SUSE-SU-2026:24422-1SUSE-SU-2026:24446-1SUSE-SU-2026:24437-1SUSE-SU-2026:24386-1SUSE-SU-2026:4706-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.40.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.40.1

opensuse advisories openSUSE-SU-2026:22167-1openSUSE-SU-2026:11880-1

  • kernel AlmaLinux 8 4.18.0-553.176.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.176.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.176.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.176.1.el8_10

almalinux advisories ALSA-2026:85773ALSA-2026:85774ALSA-2026:85321

  • kernel Rocky Linux 10 6.12.0-211.67.1.el10_2
  • kernel-rt Rocky Linux 8 4.18.0-553.176.1.rt7.517.el8_10
  • kernel Rocky Linux 8 4.18.0-553.176.1.el8_10

rocky linux advisories RLSA-2026:85321RLSA-2026:85774RLSA-2026:85773

  • kernel Azure Linux 3.0 6.6.161.1-1

azure linux advisories AZL-100496

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-89631 updated cvss 8.1

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

  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux kernel-modules-internal 6.12.0-211.67.1.el10_2 Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.67.1.el10_2, perf 6.12.0-211.67.1.el10_2, rtla 6.12.0-211.67.1.el10_2, python3-perf 6.12.0-211.67.1.el10_2, kernel-devel-matched 6.12.0-211.67.1.el10_2, kernel-64k-devel-matched 6.12.0-211.67.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.176.1.el8_10, kernel 4.18.0-553.176.1.el8_10, bpftool 4.18.0-553.176.1.el8_10, kernel-core 4.18.0-553.176.1.el8_10, kernel-tools 4.18.0-553.176.1.el8_10, python3-perf 4.18.0-553.176.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:85773
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.67.1.el10_2, kernel-64k 6.12.0-211.67.1.el10_2, kernel-core 6.12.0-211.67.1.el10_2, kernel-tools 6.12.0-211.67.1.el10_2, kernel-modules 6.12.0-211.67.1.el10_2, kernel-64k-core 6.12.0-211.67.1.el10_2, +28 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.67.1.el10_2
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.176.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.176.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.176.1.el8_10
    fixed: vendor fix RHSA-2026:85773
  • Red Hat Enterprise Linux Hidden (v. 10) kernel-modules-internal 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.67.1.el10_2
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-kvm 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-core 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-modules 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-kvm 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-core 4.18.0-553.176.1.rt7.517.el8_10, +4 more
    fixed: vendor fix RHSA-2026:85774
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.67.1.el10_2, kernel-rt-64k 6.12.0-211.67.1.el10_2, kernel-rt-core 6.12.0-211.67.1.el10_2, kernel-rt-modules 6.12.0-211.67.1.el10_2, kernel-rt-64k-core 6.12.0-211.67.1.el10_2, kernel-rt-debug-core 6.12.0-211.67.1.el10_2, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.67.1.el10_2, kernel-rt-core 6.12.0-211.67.1.el10_2, kernel-rt-modules 6.12.0-211.67.1.el10_2, kernel-rt-debug-core 6.12.0-211.67.1.el10_2, kernel-rt-modules-core 6.12.0-211.67.1.el10_2, kernel-rt-debug-modules 6.12.0-211.67.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:85321
show 2 more
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-core 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-modules 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-core 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-modules 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-modules-extra 4.18.0-553.176.1.rt7.517.el8_10, +2 more
    fixed: vendor fix RHSA-2026:85774
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
23 d ago

Exploit prediction

0.49% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.