---
id: CVE-2026-89637
title: >-
  kernel: smb: client: fix UAF and buffer leak in cifs_check_trans2() for
  malformed secondary T2 (CVE-2026-89637)
summary: >-
  A flaw was found in the Linux kernel's Server Message Block (SMB) client. When
  processing a malformed secondary TRANSACT2 response, a use-after-free (UAF)
  vulnerability and a buffer leak can occur in the `cifs_check_trans2()`
  function. Thi…
severity: high
cvss: 7
cvssVector: 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: vendor
cwe: CWE-825
vendor: Red Hat
product: Red Hat Enterprise Linux 9
affected:
  - enterprise_linux 10
  - enterprise_linux 9
  - openshift_container_platform 4
published: '2026-09-11'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T22:00:04+00:00'
source: CSAF
sourceUrl: 'https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89637.json'
references:
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89637.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89637'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532405'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89637'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89637'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89637.mbox
  - url: 'https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84'
  - url: 'https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5'
  - url: 'https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba'
tags:
  - csaf
  - vex
  - red-hat
  - cve.org
  - score-dispute
epss: 0.00588
epssPercentile: 0.46866
scores:
  vendor: 7
  cna: 9.8
ingestedAt: '2026-09-14T15:23:07.476Z'
---

## Overview

A flaw was found in the Linux kernel's Server Message Block (SMB) client. When processing a malformed secondary TRANSACT2 response, a use-after-free (UAF) vulnerability and a buffer leak can occur in the `cifs_check_trans2()` function. This can lead to a dangling buffer being reused by the demux thread, potentially allowing an attacker to achieve arbitrary code execution or cause a denial of service.

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89637.json)

**kernel: smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2** — rated Moderate by Red Hat. Released 2026-09-11, updated 2026-09-18.

Affected:

- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 9
- Red Hat OpenShift Container Platform 4

No fix planned:

- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 9
- Red Hat OpenShift Container Platform 4

Not affected:

- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 7
- Red Hat Enterprise Linux 8
- Red Hat OpenShift Container Platform 4

## Remediation

Affected