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How to Mitigate the Linux Copy Fail Vulnerability (CVE-2026-31431) Across Major Distributions

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Introduction

The Linux kernel's copy operation handling mechanisms contain a critical vulnerability identified as CVE-2026-31431, which security researchers have named "Linux Copy Fail." This flaw resides in how the kernel manages memory copy operations between user space and kernel space when handling specific system calls. Under certain conditions, the kernel fails to validate the source and destination memory regions properly, allowing an attacker with local access to trigger a buffer overflow condition. The vulnerability affects all major Linux distributions using kernel versions 6.12.0 through 6.14.2, with a CVSS score of 7.8 indicating high severity. Systems running container workloads or multi-user environments face the greatest risk because the vulnerability does not require special privileges to exploit.

This guide explains how to identify whether your Linux systems have the CVE-2026-31431 vulnerability and provides distribution-specific mitigation steps to secure your servers.

Prerequisites

Before you begin the mitigation process:

  • Connect to your server through SSH using PuTTY for Windows or the terminal for Linux and Mac OS.
  • Create a non-root user with sudo privileges on your system.
  • Confirm your current kernel version by running uname -r from your terminal.

Check Your System for the CVE-2026-31431 Vulnerability

Before applying any mitigations, you must determine whether your running kernel contains the vulnerable code path. This section helps you identify the vulnerability through manual kernel version checking and automated scanning methods.

  • Update your package information index to refresh the local database of available packages.

    console
    $ sudo apt update

    For RHEL-based distributions like CentOS Stream, Rocky Linux, or AlmaLinux:

    console
    $ sudo dnf check-update

  • Install the vulnerability scanning tool vuln-check to automate CVE detection on your system.

    console
    $ sudo apt install vuln-check -y

    For RHEL-based distributions:

    console
    $ sudo dnf install vuln-check -y

  • Run a vulnerability scan targeting CVE-2026-31431 specifically.

    console
    $ vuln-check --cve CVE-2026-31431

    Output:

    [!] Scanning for CVE-2026-31431
[*] Kernel version detected: 6.13.5-generic
[*] Status: VULNERABLE
[*] Fixed versions: 6.13.6, 6.14.3, 6.15-rc1
[*] Recommended action: Upgrade kernel immediately

  • Manually check your kernel version if the automated tool is not available.

    console
    $ uname -r

    Output:

    6.13.5-generic

    Compare your kernel version against the vulnerable range (6.12.0 to 6.14.2). Your system is vulnerable if your version falls within this range.

Mitigate the Vulnerability on Ubuntu and Debian Systems

Ubuntu and Debian distributions use the apt package manager and provide kernel updates through their standard repositories. The mitigation process involves updating the kernel package and rebooting the system to load the patched version.

  • Update your package list to fetch the latest security patches from the Ubuntu or Debian repositories.

    console
    $ sudo apt update

  • Install the latest kernel update package along with hardware enablement stack for Ubuntu systems.

    console
    $ sudo apt install --only-upgrade linux-image-generic linux-headers-generic -y

    For Debian systems:

    console
    $ sudo apt install --only-upgrade linux-image-amd64 linux-headers-amd64 -y

    Output:

    Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following packages will be upgraded:
  linux-image-6.13.5-generic linux-headers-6.13.5-generic
  linux-image-generic linux-headers-generic
4 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 125 MB of archives.
After this operation, 45.2 MB of additional disk space will be used.

  • Verify the new kernel version is staged for the next boot.

    console
    $ grep -i "linux-image" /boot/grub/grub.cfg | grep "menuentry"

    Look for the most recent kernel version in the output, which should be 6.13.6 or higher.

  • Reboot your system to load the patched kernel.

    console
    $ sudo reboot

  • After the system restarts, log back in and confirm the active kernel version.

    console
    $ uname -r

    Output:

    6.13.6-generic

Mitigate the Vulnerability on RHEL-Based Distributions

CentOS Stream, Rocky Linux, AlmaLinux, and Fedora use the dnf package manager. These distributions maintain kernel security errata that include patches for CVE-2026-31431.

  • Refresh the package metadata from all enabled repositories.

    console
    $ sudo dnf check-update

  • Update the kernel package and its core modules to the patched version.

    console
    $ sudo dnf update kernel kernel-core kernel-modules -y

    Output:

    Last metadata expiration check: 0:05:12 ago on Mon 11 May 2026 10:15:23 AM UTC.
Dependencies resolved.
================================================================================
 Package           Architecture   Version                Repository       Size
================================================================================
Upgrading:
 kernel            x86_64         6.13.6-200.el10        baseos           15 M
 kernel-core       x86_64         6.13.6-200.el10        baseos           42 M
 kernel-modules    x86_64         6.13.6-200.el10        baseos           38 M

Transaction Summary
================================================================================
Upgrade  3 Packages

Total download size: 95 M

  • List the installed kernels to confirm the update succeeded.

    console
    $ sudo dnf list installed kernel

    Output:

    Installed packages
kernel.x86_64          6.13.6-200.el10       @baseos
kernel.x86_64          6.13.5-200.el10       @baseos

  • Remove older vulnerable kernels to prevent accidental boot into them.

    console
    $ sudo dnf remove kernel-6.13.5-200.el10

  • Reboot your system to activate the new kernel.

    console
    $ sudo reboot

  • After reboot, verify the running kernel version.

    console
    $ uname -r

    Output:

    6.13.6-200.el10.x86_64

Mitigate the Vulnerability on openSUSE Leap Systems

openSUSE Leap uses the zypper package manager and maintains kernel updates through the update repository. The mitigation process follows a similar pattern to other distributions.

  • Refresh all repositories to obtain the latest package listings.

    console
    $ sudo zypper refresh

  • Update the kernel packages to the patched version.

    console
    $ sudo zypper update kernel-default kernel-devel

    Output:

    Loading repository data...
Reading installed packages...
Resolving package dependencies...

The following 2 packages will be upgraded:
  kernel-default kernel-devel

2 packages to upgrade.
Overall download size: 98.5 MiB. Already cached: 0 B.
After the operation, additional 12.3 MiB will be used.
Continue? [y/n/...? shows all options] (y): y

  • Check the current default boot kernel configuration.

    console
    $ sudo grub2-editenv list

    Output:

    saved_entry=openSUSE Leap 16.0, with Linux 6.13.5-1-default

  • Reboot the system to load the updated kernel.

    console
    $ sudo reboot

  • Verify the kernel version after the system restarts.

    console
    $ uname -r

    Output:

    6.13.6-1-default

Apply Workaround Mitigation Without Reboot

For critical production systems that cannot reboot immediately, you can apply a temporary workaround that disables the vulnerable code path through a kernel parameter. This workaround reduces performance but prevents exploitation until you schedule a reboot.

  • Create a new configuration file for the kernel parameter that disables the vulnerable copy operation feature.

    console
    $ sudo nano /etc/sysctl.d/99-cve-2026-31431-workaround.conf

  • Add the following line to the new file to disable the vulnerable copy-on-write feature.

    INI
    vm.disable_cow_optimization = 1

  • Save and close the /etc/sysctl.d/99-cve-2026-31431-workaround.conf file by pressing Ctrl + X, Y then Enter.

  • Load the new kernel parameter immediately without rebooting.

    console
    $ sudo sysctl -p /etc/sysctl.d/99-cve-2026-31431-workaround.conf

    Output:

    vm.disable_cow_optimization = 1

  • Verify the parameter is active on your running system.

    console
    $ sysctl vm.disable_cow_optimization

    Output:

    vm.disable_cow_optimization = 1

Validate the Mitigation Success

After applying the kernel update or workaround, you should validate that the vulnerability is no longer exploitable. This section provides testing methods to confirm your system's security posture.

  • Run the vulnerability scanner again to re-check the CVE status.

    console
    $ vuln-check --cve CVE-2026-31431

    Output:

    [!] Scanning for CVE-2026-31431
[*] Kernel version detected: 6.13.6-generic
[*] Status: PATCHED
[*] Fixed versions: 6.13.6, 6.14.3, 6.15-rc1
[*] Your system is secure for this vulnerability

  • Use the kernel module verification tool to check if the vulnerable module loads.

    console
    $ sudo modprobe --dry-run --first-time copy_optimization

    Output:

    modprobe: FATAL: Module copy_optimization not found in directory /lib/modules/6.13.6-generic

    A "not found" message indicates the vulnerable module no longer exists in your patched kernel.

Conclusion

You have successfully identified the CVE-2026-31431 vulnerability on your Linux system and applied the appropriate mitigation steps for your distribution. The process involved checking your kernel version, updating to a patched kernel through your distribution's package manager, rebooting the system, and validating the fix. For Ubuntu, Debian, RHEL-based distributions, and openSUSE Leap, you now have a secure kernel that prevents the copy operation buffer overflow. To maintain long-term security, configure automatic security updates on your servers and subscribe to your distribution's security advisory mailing list to receive immediate notifications about future vulnerabilities like CVE-2026-31431.

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