Patching critical vulnerabilities remains the most effective defense against server compromises. As a hosting support engineer, I've seen too many incidents that could have been prevented with timely patching. This checklist covers the vulnerability categories that demand your immediate attention across typical web hosting stacks.
Rather than chase individual CVE numbers that change weekly, this guide focuses on persistent vulnerability patterns that affect common server components. Use this as your monthly security review template.
Understanding CVE Severity Levels
Before diving into specific patches, understand how to prioritize:
Critical severity means the vulnerability allows remote code execution with no authentication, or complete system compromise. These demand immediate patching, often within 24-48 hours.
High severity typically requires authentication or user interaction but still enables significant compromise. Patch these within one week.
Medium and low severity issues should be addressed during regular maintenance windows but rarely justify emergency downtime.
Your patching urgency should also factor in exposure: a public-facing web server vulnerability is more urgent than one affecting an internal monitoring tool.
Web Server Vulnerabilities
Apache HTTP Server
Apache remains widely deployed in shared hosting environments. Key vulnerability categories to monitor:
HTTP request smuggling flaws allow attackers to bypass security controls by manipulating how requests are parsed. These often affect reverse proxy configurations.
Path traversal vulnerabilities can expose files outside the document root, potentially revealing configuration files or credentials.
Denial of service issues in HTTP/2 handling or request parsing can crash servers or consume excessive resources.
Check your current version:
apachectl -v
# or
httpd -v
Update Apache on RHEL/CentOS/AlmaLinux:
sudo dnf update httpd
sudo systemctl restart httpd
On Ubuntu/Debian:
sudo apt update
sudo apt upgrade apache2
sudo systemctl restart apache2
Nginx
Nginx vulnerabilities are less frequent but often severe when discovered:
Integer overflow bugs in HTTP/2 or HTTP/3 modules can lead to remote code execution.
Buffer overflow issues in third-party modules pose significant risk, especially in older custom builds.
DNS resolver vulnerabilities can be exploited if nginx performs upstream DNS resolution.
Verify your version:
nginx -v
Update nginx:
# RHEL-based
sudo dnf update nginx
sudo systemctl restart nginx
# Debian-based
sudo apt update
sudo apt upgrade nginx
sudo systemctl restart nginx
PHP Runtime Vulnerabilities
PHP powers the majority of shared hosting sites, making it a prime target.
Critical PHP Patterns
Remote code execution via deserialization flaws or filter bypasses represents the highest risk. These often affect core PHP functions like unserialize() or XML parsing.
File upload bypass vulnerabilities allow attackers to upload executable code despite upload restrictions.
SQL injection enablers in PDO or mysqli can affect database interaction functions.
Type confusion bugs can lead to memory corruption and arbitrary code execution.
Check installed PHP versions:
php -v
# Check all versions in cPanel/EA4
/scripts/php_get_installed_versions
Update PHP on cPanel:
# Update EasyApache 4 PHP packages
/scripts/upcp
/scripts/check_cpanel_rpms --fix
On standard Linux systems:
# RHEL-based
sudo dnf update php php-*
# Debian-based
sudo apt update
sudo apt upgrade php php-*
Important: Test applications after PHP updates. Major version updates may break compatibility.
Database Server Patches
MySQL and MariaDB
Authentication bypass vulnerabilities occasionally surface in the authentication handshake process.
SQL injection in stored procedures or specific functions can bypass application-level protections.
Privilege escalation bugs allow low-privilege database users to gain administrative access.
Replication vulnerabilities can compromise secondary servers in master-slave setups.
Check versions:
mysql --version
# or from MySQL prompt
SELECT VERSION();
Update MySQL/MariaDB:
# RHEL-based
sudo dnf update mysql-server mariadb-server
sudo systemctl restart mysqld
# or
sudo systemctl restart mariadb
# Debian-based
sudo apt update
sudo apt upgrade mysql-server mariadb-server
sudo systemctl restart mysql
Always back up databases before updating the server software.
PostgreSQL
PostgreSQL vulnerabilities are rare but serious when they occur:
Command injection in extensions or procedural languages.
Memory corruption in query parsing or execution.
Authorization bypass allowing unauthorized data access.
Update PostgreSQL:
# RHEL-based
sudo dnf update postgresql postgresql-server
sudo systemctl restart postgresql
# Debian-based
sudo apt update
sudo apt upgrade postgresql postgresql-contrib
sudo systemctl restart postgresql
OpenSSL and TLS Libraries
SSL/TLS vulnerabilities affect every encrypted connection your server handles.
Remote code execution vulnerabilities in certificate parsing or handshake processing are critical.
Information disclosure flaws can leak private keys or session data.
Denial of service attacks against specific cipher suites or protocol versions.
Check OpenSSL version:
openssl version -a
Update OpenSSL:
# RHEL-based
sudo dnf update openssl openssl-libs
# Debian-based
sudo apt update
sudo apt upgrade openssl libssl-dev
After OpenSSL updates, restart all services using it: Apache, Nginx, Postfix, Dovecot, FTP servers, and SSH.
sudo systemctl restart httpd nginx postfix dovecot sshd
Control Panel Vulnerabilities
cPanel & WHM
cPanel releases security updates regularly through the update system:
Cross-site scripting (XSS) in the web interface can compromise administrator sessions.
Authentication bypass vulnerabilities are rare but devastating.
Privilege escalation allowing reseller or user accounts to gain root access.
API vulnerabilities in UAPI or API2 endpoints.
Update cPanel:
/scripts/upcp
Enable automatic updates in WHM:
- WHM → Server Configuration → Update Preferences
- Set "cPanel & WHM Updates" to automatic for the RELEASE tier
Plesk
Plesk vulnerabilities often affect the management interface:
SQL injection in admin panel functions.
Path traversal allowing file system access.
Command injection in system utilities.
Update Plesk:
plesk installer update
WordPress Core and Plugin Vulnerabilities
WordPress sites are frequent attack targets due to widespread deployment.
Core WordPress
SQL injection in core database queries.
Cross-site scripting in comment handling or post editor.
Authentication bypass in REST API or XML-RPC endpoints.
Object injection in serialization functions.
Update WordPress core via WP-CLI:
wp core update --path=/home/username/public_html
wp core update-db --path=/home/username/public_html
High-Risk Plugin Categories
Certain plugin types have higher vulnerability rates:
Contact forms with file upload capabilities.
SEO plugins with complex database operations.
Page builders with custom code execution features.
Backup plugins with file system access.
Security plugins themselves can introduce vulnerabilities.
Update all plugins:
wp plugin update --all --path=/home/username/public_html
List plugins needing updates:
wp plugin list --update=available --path=/home/username/public_html
SSH and Remote Access
OpenSSH vulnerabilities can allow authentication bypass or remote code execution.
Key exchange vulnerabilities may enable man-in-the-middle attacks.
Privilege escalation in SSH daemon configuration.
Check SSH version:
ssh -V
Update OpenSSH:
# RHEL-based
sudo dnf update openssh openssh-server
sudo systemctl restart sshd
# Debian-based
sudo apt update
sudo apt upgrade openssh-server openssh-client
sudo systemctl restart ssh
Email Server Security
Postfix and Exim
Remote code execution via email header parsing or attachment processing.
SMTP smuggling allowing spam relay abuse.
Authentication bypass in SASL mechanisms.
Update Postfix:
sudo dnf update postfix # RHEL
sudo apt upgrade postfix # Debian
sudo systemctl restart postfix
Update Exim (common in cPanel):
# cPanel handles this via upcp
/scripts/upcp --force
Dovecot
Remote code execution in IMAP/POP3 parsing.
Authentication bypass vulnerabilities.
Directory traversal in mailbox access.
Update Dovecot:
sudo dnf update dovecot # RHEL
sudo apt upgrade dovecot-core dovecot-imapd # Debian
sudo systemctl restart dovecot
Kernel Vulnerabilities
Linux kernel patches address privilege escalation and container escape vulnerabilities.
Local privilege escalation allowing unprivileged users to gain root.
Container escape vulnerabilities affecting Docker or LXC.
Use-after-free bugs in kernel subsystems.
Check kernel version:
uname -r
Update kernel:
# RHEL-based
sudo dnf update kernel
# Reboot required
# Debian-based
sudo apt update
sudo apt upgrade linux-image-*
# Reboot required
Kernel updates always require a reboot to take effect. Schedule downtime accordingly.
Patch Management Checklist
Use this monthly workflow:
Week 1: Monitor and plan - Subscribe to security mailing lists for your stack components - Review vendor security advisories - Identify critical and high-severity issues affecting your systems - Schedule maintenance windows
Week 2: Test environment - Apply patches to staging or test servers first - Run application test suites - Verify service functionality - Document any issues or compatibility problems
Week 3: Production deployment - Create full backups before patching - Apply patches during low-traffic windows - Monitor error logs and performance metrics - Have rollback plan ready
Week 4: Verification - Confirm patches applied successfully - Run vulnerability scanners - Review monitoring for anomalies - Document the patching cycle
Automated Patch Management
For RHEL-based systems, configure automatic security updates:
sudo dnf install dnf-automatic
sudo systemctl enable --now dnf-automatic.timer
Edit /etc/dnf/automatic.conf:
[commands]
apply_updates = yes
upgrade_type = security
For Debian/Ubuntu:
sudo apt install unattended-upgrades
sudo dpkg-reconfigure -plow unattended-upgrades
Caution: Automatic updates can occasionally break services. Monitor closely and maintain good backups.
Conclusion
Critical vulnerability patching is not optional—it is the foundation of server security. Establish a regular patching cadence, prioritize based on severity and exposure, and always maintain current backups before applying updates. The categories outlined here represent the most common attack vectors against web hosting infrastructure. Stay subscribed to security advisories for your specific software stack, test patches in staging environments when possible, and act quickly when critical vulnerabilities are announced. Your proactive patching discipline directly determines your server's security posture.