---
title: "CVE-2026-89639: Linux Kernel - Cache Invalidation Issue in CIFS Truncate"
description: "Linux kernel contains a cache invalidation issue in cifs_do_truncate() caused by improper cache handling without i_rwsem, letting attackers cause stale cached data to be served, exploit requires file truncation with O_TRUNC flag."
url: https://panop.io/threat-heartbeat/CVE-2026-89639/
---

# CVE-2026-89639 Linux Kernel - Cache Invalidation Issue in CIFS Truncate

Linux kernel contains a cache invalidation issue in cifs\_do\_truncate() caused by improper cache handling without i\_rwsem, letting attackers cause stale cached data to be served, exploit requires file truncation with O\_TRUNC flag.

CVSS base score 7.1 /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-2026-89639)

## Details

Type

Cache Invalidation Issue in CIFS Truncate

Impact

Information Disclosure

CVSS vector

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

Published

11 September 2026

Updated

15 October 2026

## Vendor fix

Update to the latest Linux kernel version containing the fix.

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-2026-89639](https://nvd.nist.gov/vuln/detail/CVE-2026-89639)
- [https://git.kernel.org/stable/c/364b183230586a62660a7280c1eb20138338eeb5](https://git.kernel.org/stable/c/364b183230586a62660a7280c1eb20138338eeb5)
- [https://git.kernel.org/stable/c/81fc3868a7f726980ff845c1d0d271051e5f0f45](https://git.kernel.org/stable/c/81fc3868a7f726980ff845c1d0d271051e5f0f45)
- [https://git.kernel.org/stable/c/8b9b10fe5b8b492b27b9f4546742ea541a650213](https://git.kernel.org/stable/c/8b9b10fe5b8b492b27b9f4546742ea541a650213)

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## 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

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