CVE-2026-89745
Received Received - Intake

Debugfs Lockdown Bypass via mmap_prepare

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: debugfs: Fix lockdown check for mmap_prepare Commit 651fdda8406d ("relay: update relay to use mmap_prepare") changed the `mmap` file operation to `mmap_prepare` for relayfs, but the lockdown check in debugfs was not updated accordingly. This prevents debugfs from being locked down when the kernel is in integrity mode if a file uses `mmap_prepare` but not `mmap`. Since the conversion to `mmap_prepare` across the kernel is not yet complete, update the lockdown check to look for both `mmap` and `mmap_prepare` to ensure comprehensive coverage.

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Meta Information

Published
2026-09-11
Last Modified
2026-09-11
Generated
2026-09-12
AI Q&A
2026-09-11
EPSS Evaluated
N/A
NVD
CVE-2026-89745
EUVD
EUVD-2026-76657

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a missing update to the lockdown check in debugfs. When the kernel is in integrity mode, debugfs should be locked down to prevent unauthorized access. However, a recent change replaced the mmap file operation with mmap_prepare in relayfs without updating the corresponding lockdown check in debugfs. This oversight allows debugfs to remain unlocked if a file uses mmap_prepare but not mmap, potentially exposing sensitive data or enabling unauthorized modifications.

Detection Guidance

This vulnerability is specific to the Linux kernel's debugfs and relayfs components. Detection requires checking kernel version and debugfs state. Inspect kernel logs for relayfs or debugfs errors using: dmesg | grep -i debugfs or dmesg | grep -i relayfs. Verify if your kernel is affected by checking the version with uname -a and comparing against patched versions.

Impact Analysis

If you use a Linux system with debugfs enabled and the kernel in integrity mode, this vulnerability could allow an attacker with local access to bypass security restrictions. This might lead to unauthorized access to kernel memory, privilege escalation, or the ability to modify system files, compromising the integrity and confidentiality of your system.

Compliance Impact

This vulnerability could impact compliance with GDPR and HIPAA by potentially exposing sensitive data or allowing unauthorized system modifications. GDPR requires protecting personal data integrity and confidentiality, while HIPAA mandates safeguarding protected health information. A successful exploit could violate these requirements, leading to legal and regulatory penalties.

Mitigation Strategies

Update your Linux kernel to the latest stable version that includes the fix for CVE-2026-89745. If immediate patching is not possible, consider disabling debugfs or relayfs if not required, or apply kernel lockdown restrictions manually via kernel command line parameters like lockdown=integrity.

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