Protecting Your Server from the “Copy Fail” Kernel Vulnerability (CVE-2026-31431)

A high-severity vulnerability, CVE-2026-31431 (also known as “Copy Fail”), has been identified in the Linux Kernel. This flaw resides in the AF_ALG socket family and can allow a local user to gain unauthorized root access by manipulating the kernel page cache.

Step 1: Identify Your Kernel Configuration

The fix depends on whether the vulnerable component is a module or built directly into your kernel. Run the following command in your terminal:

grep CONFIG_CRYPTO_USER_API_AEAD /boot/config-$(uname -r)

Step 2: Apply the Mitigation

Option A: Module Blacklist (If result is =m)

This is standard for Ubuntu and Debian systems. This prevents the vulnerable module from loading into memory.

# Disable the module from future loads
echo "install algif_aead /bin/true" > /etc/modprobe.d/cve-2026-31431.conf

# Unload the module if it is currently active
rmmod algif_aead

Option B: Bootloader Blacklist (If result is =y)

Standard for CloudLinux, AlmaLinux, and RHEL. Since the component is built-in, you must use grubby to disable the specific initialization call at boot time.

# Apply the recommended mitigation via grubby
grubby --update-kernel=ALL --args="initcall_blacklist=algif_aead_init"

# Reboot the server to apply the changes
reboot

Verify Your Protection

After applying the fix and rebooting (if using Option B), run this check to confirm the vulnerability is closed:

1. Check Kernel Logs (CloudLinux/RHEL Only)

dmesg | grep "algif_aead_init blacklisted"

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