---
title: "CVE-2026-89638: Linux Kernel - Broken Access Control"
description: "Linux kernel contains a broken access control vulnerability caused by improper clearing of setuid/setgid bits on write with cifsacl/modefromsid/posix extensions, letting attackers retain setuid/setgid bits unexpectedly, exploit requires usage of affected CIFS mount options."
url: https://panop.io/threat-heartbeat/CVE-2026-89638/
---

# CVE-2026-89638 Linux Kernel - Broken Access Control

Linux kernel contains a broken access control vulnerability caused by improper clearing of setuid/setgid bits on write with cifsacl/modefromsid/posix extensions, letting attackers retain setuid/setgid bits unexpectedly, exploit requires usage of affected CIFS mount options.

CVSS base score 7.8 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Required

EPSS

0.17% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-89638)

## Details

Type

Broken Access Control

Impact

Privilege Escalation

CVSS vector

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

Published

11 September 2026

Updated

15 October 2026

## Vendor fix

Update to the latest Linux kernel version containing the fix for proper clearing of setuid/setgid bits on CIFS mounts.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-89638](https://nvd.nist.gov/vuln/detail/CVE-2026-89638)
- [https://git.kernel.org/stable/c/b10015807e4c628095d1d1d1c9307efc8cdd9e1b](https://git.kernel.org/stable/c/b10015807e4c628095d1d1d1c9307efc8cdd9e1b)
- [https://git.kernel.org/stable/c/b8e5dc4f95e5484159b343903f302eb6d783f2e6](https://git.kernel.org/stable/c/b8e5dc4f95e5484159b343903f302eb6d783f2e6)
- [https://git.kernel.org/stable/c/58b23fc9fb580432470d6c5da3c1e5660dba9fbc](https://git.kernel.org/stable/c/58b23fc9fb580432470d6c5da3c1e5660dba9fbc)
- [https://git.kernel.org/stable/c/69bfe810ecd1e0387d8975d711cd326341d13c6e](https://git.kernel.org/stable/c/69bfe810ecd1e0387d8975d711cd326341d13c6e)

[← All CVEs](https://panop.io/threat-heartbeat/)

## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

[Book a demo](https://panop.io/demo)