---
id: CVE-2026-89640
title: >-
  kernel: cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0
  (CVE-2026-89640)
summary: >-
  A flaw was found in the Linux kernel's Common Internet File System (CIFS)
  implementation. When performing a file range remapping operation with a zero
  length, an integer underflow can occur if the offset exceeds the file size.
  This can lea…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cvssSource: vendor
cwe: CWE-787
vendor: Red Hat
product: Red Hat Enterprise Linux 9
affected:
  - enterprise_linux 10
  - enterprise_linux 8
  - enterprise_linux 9
  - openshift_container_platform 4
published: '2026-09-11'
updated: '2026-09-15'
sourceUpdated: '2026-09-15T08:13:26+00:00'
source: CSAF
sourceUrl: 'https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89640.json'
references:
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89640.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89640'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532516'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89640'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89640'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89640.mbox
  - url: 'https://git.kernel.org/stable/c/f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4'
  - url: 'https://git.kernel.org/stable/c/7f62817fe049b0f3652518c1ba72631ec1e0a322'
  - url: 'https://git.kernel.org/stable/c/b098f5e5858797827666e6cd73033f52fc39b5f6'
  - url: 'https://git.kernel.org/stable/c/c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028'
  - url: 'https://git.kernel.org/stable/c/b057ca17b656345d04669cb87f2aff9b31d873db'
  - url: 'https://git.kernel.org/stable/c/6c322f5cf7476ded7a9a20f7be72462065a03c68'
tags:
  - csaf
  - vex
  - red-hat
  - cve.org
epss: 0.00126
epssPercentile: 0.02621
scores:
  vendor: 5.5
  cna: 7.1
ingestedAt: '2026-09-14T15:23:07.450Z'
---

## Overview

A flaw was found in the Linux kernel's Common Internet File System (CIFS) implementation. When performing a file range remapping operation with a zero length, an integer underflow can occur if the offset exceeds the file size. This can lead to corruption of the byte count in file system control requests, potentially causing unexpected behavior or data integrity issues. The vulnerability is resolved by correctly validating the offset against the file size before calculating the length, preventing the underflow.

## Vendor advisories

- **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89640.json)

**kernel: cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0** — rated Low by Red Hat. Released 2026-09-11, updated 2026-09-15.

Affected:

- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
- Red Hat OpenShift Container Platform 4

No fix planned:

- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
- Red Hat OpenShift Container Platform 4

Not affected:

- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 7

## Remediation

Fix deferred