CVE-2026-89642

Received Received - Intake

Pagecache Size Extension Issue in Linux Kernel CIFS

Publication date: 2026-09-11

Last updated on: 2026-09-11

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: cifs: call pagecache_isize_extended() in cifs_setsize() when extending cifs_setsize() calls truncate_pagecache() but skips pagecache_isize_extended() on extension. truncate_setsize() shows the correct pattern: i_size_write(inode, newsize); if (newsize > oldsize) pagecache_isize_extended(inode, oldsize, newsize); truncate_pagecache(inode, newsize); pagecache_isize_extended() zeroes the tail of the page straddling old EOF. Without it, dirty bytes in that region can be written back to the server, exposing stale data in the newly extended range.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-09-11

Last Modified

2026-09-11

Generated

2026-09-12

AI Q&A

2026-09-12

EPSS Evaluated

N/A

NVD

CVE-2026-89642

EUVD

EUVD-2026-76554

Affected Vendors & Products

Vendor	Product	Version / Range
linux_kernel	cifs	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel's CIFS (Common Internet File System) module occurs when extending file sizes. The function cifs_setsize() calls truncate_pagecache() but omits pagecache_isize_extended() during file extension. This omission can lead to stale data being written back to the server if dirty bytes exist in the extended file range.

Detection Guidance

This vulnerability is specific to the Linux kernel's CIFS (Common Internet File System) implementation. Detection requires checking if your system is running a vulnerable kernel version. Use uname -a to check the kernel version and verify if it includes the affected CIFS code. If you are running a kernel version prior to the fix, the system is likely vulnerable.

Impact Analysis

If exploited, this vulnerability could allow an attacker to access or overwrite stale data in extended file regions. This might result in unauthorized information disclosure or data corruption when files are resized on a CIFS-mounted filesystem.

Compliance Impact

This vulnerability could potentially violate data integrity and confidentiality requirements in GDPR and HIPAA. Exposure of stale data during file operations may lead to unauthorized access to personal or sensitive information, compromising compliance with these regulations.

Mitigation Strategies

Immediately update your Linux kernel to the latest patched version that includes the fix for this CIFS vulnerability. If updating is not immediately possible, consider disabling the CIFS module temporarily or restricting access to CIFS shares until the update is applied.

Hi! I’m here to help you understand CVE-2026-89642. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70