Real-Time Kernel Vulnerabilities (CVE-2025-68741 & CVE-2026-23191)

 

Stop chasing CVEs. Learn to check, fix, and mitigate kernel flaws (like CVE-2025-68741) in AlmaLinux/Rocky Linux 8, RHEL. Includes a bash script, iptables backup plan, and a book that teaches you to find zero-days yourself. 

The Situation: When Your Real-Time Kernel Needs a Real-Time Fix

On April 25, 2026, a security advisory (RLSA-2026:9135) was published for Rocky Linux (and AlmaLinux) 8. It addressed two Linux kernel vulnerabilities:

• CVE-2025-68741 (CVSS 7.3 High): An improper freeing of memory (CWE-763) in the qla2xxx SCSI driver.

• CVE-2026-23191 (CVSS 7.1 High): A race condition (CWE-367) in the aloop (ALSA sound loopback) driver during PCM trigger operations.

Why this matters long-term: Race conditions and improper memory freeing are archetypal kernel bugs. They will appear again in different drivers, different kernel versions, and different CVEs. Learning the pattern today protects you tomorrow.

How to Check if Your AlmaLinux / Rocky Linux 8 / RHEL System is Vulnerable

Run these commands as root or with sudo. We’ll focus on the real-time kernel (kernel-rt), which is common in financial trading, telecom, industrial control, and audio production.

bash

# 1. Check your current kernel version
uname -r

# 2. Compare against the fixed version (from the advisory)
# Fixed version: 4.18.0-553.120.1.rt7.461.el8_10
echo "Your kernel: $(uname -r)"
echo "Fixed kernel: 4.18.0-553.120.1.rt7.461"

# 3. See if your system has the RT kernel installed
rpm -qa | grep kernel-rt

# 4. Check if the specific vulnerable driver is loaded (qla2xxx is for QLogic fibre channel)
lsmod | grep qla2xxx

# 5. The race condition affects the sound loopback module. Check if it's loaded.
lsmod | grep snd_aloop

If uname -r shows a version older than 4.18.0-553.120.1.rt7.461, you are vulnerable.

Automation Script to Apply the Fix (Bash – Alma Linux / Rocky Linux / RHEL)

This script detects your distribution and applies the correct kernel update. It handles the race condition (CVE-2026-23191) by forcing a full kernel update, which is the only complete fix for such flaws.

bash

#!/bin/bash
# Kernel Security Fix Script for CVE-2025-68741, CVE-2026-23191
# Compatible with AlmaLinux, Rocky, RHEL (YUM/DNF) and Debian/Ubuntu (APT)

set -e

if [ "$EUID" -ne 0 ]; then
  echo "Please run as root (use sudo)."
  exit 1
fi

echo "[*] Checking for vulnerable kernel version..."
CURRENT=$(uname -r)
echo "[!] Current kernel: $CURRENT"

# Detect OS
if [ -f /etc/redhat-release ]; then
  echo "[*] RHEL-based system detected. Updating kernel via DNF/YUM."
  dnf update kernel kernel-rt -y
elif [ -f /etc/debian_version ]; then
  echo "[*] Debian-based system detected. Updating kernel via APT."
  apt update
  apt install linux-image-generic linux-headers-generic -y
else
  echo "Unsupported distribution. Please update kernel manually."
  exit 1
fi

echo "[✓] New kernel packages installed."
echo "[!] A reboot is required to load the patched kernel."
read -p "Reboot now? (y/n): " -n 1 -r
echo
if [[ $REPLY =~ ^[Yy]$ ]]; then
  reboot
else
  echo "Please reboot manually as soon as possible."
fi

Pro tip: Save this script as kernel-update.sh, make it executable (chmod +x kernel-update.sh), and run it every time you see a kernel CVE.

Alternative Mitigation (If You Cannot Reboot or Update Now)

A kernel module update always requires a reboot (or kpatch/kGraft live patching). If live patching isn’t available, here are temporary mitigations – they reduce risk but don’t fully patch the flaws:

1. Mitigate qla2xxx improper free (CVE-2025-68741) – Blacklist the driver if not needed:

bash

# Only do this if you do NOT use QLogic fibre channel storage.
echo "blacklist qla2xxx" >> /etc/modprobe.d/blacklist-security.conf
# Remove if currently loaded
modprobe -r qla2xxx

2. Mitigate snd_aloop race condition (CVE-2026-23191) – Restrict access:

bash

# Block the module entirely if you don't need virtual audio loops
echo "blacklist snd_aloop" >> /etc/modprobe.d/blacklist-security.conf

# Or use iptables to limit local access to audio devices (limited effect)
iptables -A OUTPUT -m owner --uid-owner pulse -j ACCEPT
iptables -A OUTPUT -j DROP -m comment --comment "CVE-2026-23191 mitigation (partial)"

3. For high-stakes real-time systems: Use chroot or container isolation to limit an attacker’s local privilege escalation path. Race conditions often require local access – so lock down local users.

Why This Book Is Better Than 100 CVEs

You saw the script above. It fixes this CVE. But what about the next one? The one that isn’t published yet. The one hiding in a driver you just compiled.

This script solves a single CVE.

Practical Binary Analysis: Build Your Own Linux Tools for Binary Instrumentation, Analysis, and Disassembly solves the process of finding and fixing CVEs yourself.

Page 185–210: Binary instrumentation to detect memory corruption (like CVE-2025-68741) at runtime.

Chapter 7: Dynamic taint tracking to identify race conditions (exactly CVE-2026-23191) without crashing the kernel.

It’s not a patch. It’s a craft – you learn to build your own fuzzers, disassemblers, and binary tools.

Grab it here: Practical Binary Analysis on Amazon

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.).

Conclusion:

You have three choices right now:

• Patch now – use the script above, reboot, and move on.

• Mitigate now – use blacklist and iptables if you cannot reboot.

• Master the craft – buy the book and stop waiting for security advisories.