How to Handle Critical Linux Kernel Flaws (Like the Recent Ubuntu FIPS Update)

 

Stop chasing patch dates. Learn to check, fix, and mitigate Linux kernel vulnerabilities (CVE-2024-36347, EntrySign) on Ubuntu, Rocky, and SUSE. Includes a hands-on lab, automation script, and iptables fallback for admins who can't reboot now. 

On April 17, 2026, Canonical released USN-8179-2 for Ubuntu 24.04 LTS FIPS kernels. It fixed over 100 CVEs, including the nasty EntrySign (CVE-2024-36347) — a flaw in AMD Zen microcode signature verification.

But here's the thing: if you only read that news, you learned nothing useful for next month's kernel panic. This guide turns that one-time alert into a repeatable playbook for any Linux kernel vulnerability.

2. How to Check If You Are Vulnerable (Actual Commands)

Run these on Ubuntu 24.04 LTS (with FIPS kernel):

bash

# Check your current kernel version
uname -r

# For generic FIPS – vulnerable if lower than 6.8.0-110.110+fips2
# For AWS FIPS – vulnerable if lower than 6.8.0-1052.55+fips1
# For GCP FIPS – vulnerable if lower than 6.8.0-1054.57+fips1

# Quick check for EntrySign (AMD only)
if grep -q "AMD" /proc/cpuinfo; then
  echo "AMD CPU present. Check microcode:"
  grep "microcode" /proc/cpuinfo | head -1
else
  echo "Not an AMD system – EntrySign not applicable"
fi

# See if your system has pending kernel updates
apt list --upgradable 2>/dev/null | grep -E "linux-(image|headers)"

For Rocky Linux / AlmaLinux 9:

bash

# Check kernel
uname -r
# Compare against https://access.redhat.com/security/cve/cve-2024-36347
dnf check-update kernel

For SUSE Linux Enterprise Server 15 SP5:

bash

uname -r
zypper list-updates | grep kernel

3. Automation Script to Apply the Fix (Bash – Major Distros)

Save this as fix-linux-kernel.sh and run as root.

bash

#!/bin/bash
# Evergreen kernel vulnerability fixer – Ubuntu, Rocky, SUSE
# Usage: sudo bash fix-linux-kernel.sh

set -e

detect_os() {
    if [ -f /etc/os-release ]; then
        . /etc/os-release
        OS=$ID
        VER=$VERSION_ID
    else
        echo "Cannot detect OS. Exiting."
        exit 1
    fi
}

backup_grub() {
    cp /etc/default/grub /etc/default/grub.backup.$(date +%Y%m%d)
    echo "Grub backup created."
}

update_ubuntu() {
    apt update
    apt upgrade -y linux-image-$(uname -r | cut -d- -f1)-fips linux-headers-$(uname -r | cut -d- -f1)-fips
    apt autoremove -y
}

update_rocky() {
    dnf update -y kernel kernel-devel kernel-headers
}

update_suse() {
    zypper refresh
    zypper update -y kernel-default kernel-devel
}

check_reboot_needed() {
    if [ -f /var/run/reboot-required ]; then
        echo "Reboot required. Run: systemctl reboot"
    else
        echo "No reboot flag found, but always reboot after kernel update."
    fi
}

main() {
    detect_os
    echo "OS detected: $OS $VER"
    backup_grub

    case $OS in
        ubuntu)
            update_ubuntu
            ;;
        rocky|almalinux|rhel)
            update_rocky
            ;;
        suse|opensuse-leap)
            update_suse
            ;;
        *)
            echo "Unsupported OS. Manual update required."
            exit 1
            ;;
    esac

    echo "Kernel updated. Recompile third-party modules if any."
    check_reboot_needed
}

main

Make it executable

bash

chmod +x fix-linux-kernel.sh
sudo ./fix-linux-kernel.sh

4. Alternative Mitigation (If You Can't Update Now)

Sometimes you can't reboot – production, change freeze, whatever. Here's what you can do immediately without a reboot.

For EntrySign (AMD microcode) – No direct iptables fix, but you can limit local privilege escalation

bash

# Restrict who can load microcode (requires reboot? no – but limits exposure)
# Only allow root to write to microcode interface
chmod 0600 /sys/devices/system/cpu/microcode/reload

General kernel memory corruption mitigation (works for many CVEs)

Using iptables to block known attack vectors (e.g., unexpected ICMP, SMB, or specific ports):

bash

# Block SMB (445) if you don't need it – common kernel bypass target
iptables -A INPUT -p tcp --dport 445 -j DROP
iptables -A INPUT -p udp --dport 445 -j DROP

# Block unusual ICMP types (mitigates some IPv4/IPv6 kernel bugs)
iptables -A INPUT -p icmp --icmp-type 13 -j DROP   # timestamp request
iptables -A INPUT -p icmp --icmp-type 17 -j DROP   # address mask request

# Save rules (Ubuntu/Debian)
apt install iptables-persistent -y
netfilter-persistent save

Using AppArmor to confine vulnerable kernel modules:

bash

# Put a vulnerable driver (e.g., v4l2, btusb) in complain mode to log but not block
aa-complain /etc/apparmor.d/* 2>/dev/null
# Then enforce only on critical paths
aa-enforce /etc/apparmor.d/usr.sbin.tcpdump

Using sysctl hardening (reduces kernel attack surface):

bash

cat >> /etc/sysctl.d/99-kernel-hardening.conf << EOF
# Disable bpf() for unprivileged users (kills many kernel exploits)
kernel.unprivileged_bpf_disabled=1
# Restrict kernel pointer access
kernel.kptr_restrict=2
# Disable core dumps for setuid
fs.suid_dumpable=0
EOF
sysctl -p /etc/sysctl.d/99-kernel-hardening.conf

Suggested reding: 

Linux Kernel Programming:  by  Kaiwan N Billimoria - Amazon

Why this matter ?

The Ubuntu notice warns: “ABI change requires you to recompile and reinstall all third party kernel modules.”

If you don't know how to write or fix a kernel module, you're stuck. This book teaches you:

• How to build kernel modules that survive ABI bumps

• Debugging oops and panics after updates

• Writing secure modules (avoiding CVEs like the 100+ listed)

Without this skill, every kernel update becomes a gamble. With it, you own your stack.

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Affiliate disclosure: As an Amazon Associate, I earn from qualifying purchases. This helps me keep writing in-depth security guides – at no extra cost to you.)