We are issuing an important notice regarding a kernel-level vulnerability affecting CloudLinux systems.

Official advisory:
https://blog.cloudlinux.com/cve-2026-31431-copy-fail-mitigation-and-patches

Vulnerability ID: CVE-2026-31431
Severity: High
Component: Linux Kernel (copy_file_range system call)

What is the issue?

This issue is related to the Linux kernel’s copy_file_range function, which is used internally for efficient file copying.

Due to a flaw in the kernel implementation, file copy operations may behave incorrectly, leading to:

• Silent data corruption
• Incomplete file copies
• Unexpected failures during file operations

This issue is particularly critical because it may not generate visible errors, making it difficult to detect.

What is the risk?

• Corrupted backups without warning
• Broken website files or application data
• Data inconsistency during migrations
• Integrity issues in storage and backup systems

This directly impacts hosting environments using backup systems such as JetBackup, rsync, or any tool relying on kernel-level file copying.

Who is affected?

• CloudLinux servers running affected kernel versions
• Systems performing frequent file operations (backups, restores, migrations)
• cPanel/WHM servers using CloudLinux

Actions taken by HostRainbow

• Reviewed all CloudLinux-based servers
• Applied patched kernel updates where available
• Verified backup integrity and file consistency
• Enabled additional monitoring for file operations

All managed HostRainbow servers are being secured and monitored.

Required actions for unmanaged or self-managed servers

If you are managing your own server, follow these steps immediately:

1. Update CloudLinux packages and kernel

dnf update -y

2. Reboot the server (Required)

Apply the updated kernel:

reboot

3. Verify kernel version

uname -r

Ensure the kernel version matches the patched release provided by CloudLinux.

4. Apply CloudLinux mitigation (if update not yet applied)

CloudLinux recommends disabling the use of copy_file_range in affected environments until fully patched.

5. Verify backups and data integrity

• Check recent backups for corruption
• Test restore points
• Re-run backups where necessary

6. Monitor file operations

• Validate file sizes after copy
• Use checksums (md5/sha256) to verify integrity
• Watch for unusual behavior in backup or migration tools

Important note

If your server was running an affected kernel, there is a risk that file operations performed during that period may be unreliable.

Recommended:

• Re-verify critical website and database files
• Re-run recent backups
• Audit important data for consistency

Need assistance?

If you need help updating your server, verifying data integrity, or applying mitigation steps, our support team is available to assist.

Team HostRainbow