Jessica Brown

Penetration testing, often referred to as "pen testing," is a proactive cybersecurity assessment that simulates real-world attacks on a system, network, or application to identify vulnerabilities. This process is an essential part of an organization’s overall security strategy, enabling them to detect and address weaknesses before malicious actors exploit them. In this guide, we’ll cover the fundamentals of penetration testing, including its purpose, methodologies, tools, and best practices. What Is Penetration Testing? Penetration testing is an authorized, simulated attack against an organization’s assets to evaluate the security posture. The goal is to: Identify vulnerabilities in systems, networks, or applications. Assess the potential impact of a successful exploit. Provide actionable recommendations to mitigate risks. Pen testing helps organizations comply with regulatory standards, protect sensitive data, and maintain trust with their customers. Types of Penetration Testing Penetration testing can target various aspects of an organization’s environment: Network Penetration Testing: Focuses on identifying vulnerabilities in network infrastructure, including firewalls, routers, and switches. Example vulnerabilities: misconfigured firewalls, open ports, or outdated protocols. Web Application Penetration Testing: Targets vulnerabilities in web applications, such as SQL injection, cross-site scripting (XSS), or insecure authentication mechanisms. Wireless Penetration Testing: Evaluates the security of wireless networks. Example vulnerabilities: weak Wi-Fi encryption, rogue access points, or misconfigured SSIDs. Social Engineering Testing: Simulates human-based attacks, such as phishing or pretexting, to evaluate staff awareness and response to threats. Physical Penetration Testing: Involves attempting to gain physical access to restricted areas or hardware. Example scenarios: bypassing locks or accessing sensitive devices. Mobile Application Penetration Testing: Focuses on vulnerabilities in mobile apps, such as insecure data storage or improper session handling. The Penetration Testing Process Penetration testing follows a structured approach, often modeled on established methodologies like the PTES (Penetration Testing Execution Standard) or OWASP (Open Web Application Security Project) Testing Guide: Planning and Reconnaissance: Define the scope and objectives. Gather information about the target system (e.g., IP addresses, domain names, or publicly available data). Scanning: Use tools to identify active services, open ports, and vulnerabilities. Example tools: Nmap, Nessus, or OpenVAS. Exploitation: Attempt to exploit identified vulnerabilities to gain unauthorized access or privileges. Example exploits: gaining access through an outdated software version or leveraging weak credentials. Post-Exploitation: Assess the extent of access gained and determine the potential impact. Example actions: accessing sensitive files, escalating privileges, or maintaining persistence. Reporting: Document findings, including vulnerabilities, proof of concept, and recommendations for remediation. Deliver a comprehensive report to stakeholders. Remediation and Retesting: Address identified vulnerabilities and retest to verify fixes. Tools for Penetration Testing Pen testers use a variety of tools during assessments. Some common categories include: Reconnaissance Tools: Example: Maltego, Shodan. Scanning Tools: Example: Nmap, Nessus, OpenVAS. Exploitation Tools: Example: Metasploit, Cobalt Strike. Web Application Tools: Example: Burp Suite, OWASP ZAP. Wireless Testing Tools: Example: Aircrack-ng, Kismet. Password Cracking Tools: Example: Hashcat, John the Ripper. Skills and Knowledge Needed To become proficient in penetration testing, you need a combination of technical and soft skills: Technical Skills: Strong knowledge of operating systems (Linux and Windows). Understanding of networking concepts and protocols (TCP/IP, DNS, etc.). Familiarity with programming and scripting languages (Python, Bash, etc.). Experience with cybersecurity tools and frameworks. Soft Skills: Critical thinking and problem-solving. Communication skills for documenting findings and presenting to non-technical stakeholders. Attention to detail. Best Practices for Penetration Testing Get Proper Authorization: Always obtain written permission from stakeholders before starting a penetration test. Follow a Defined Methodology: Use standards like PTES, OWASP, or NIST to guide your testing process. Limit Scope Creep: Clearly define the scope to avoid unauthorized testing or accidental disruption. Document Everything: Keep records of findings, actions, and results for reporting and future reference. Stay Ethical: Adhere to ethical guidelines and avoid unnecessary damage or disruption. Keep Skills Updated: Stay informed about emerging threats, vulnerabilities, and tools. Penetration testing is a critical component of cybersecurity, helping organizations proactively identify and mitigate vulnerabilities. By understanding the fundamentals, methodologies, tools, and best practices, both beginners and experienced professionals can contribute effectively to securing digital assets. Whether you’re a business owner looking to improve your defenses or an aspiring cybersecurity professional, penetration testing is a valuable skill to master.

Uploading large files to a website can fail due to server-side limitations on file size. This issue is typically caused by default configurations of web servers like Nginx or Apache, or by PHP settings for sites using PHP. This guide explains how to adjust these settings and provides detailed examples for common scenarios. For Nginx Nginx limits the size of client requests using the client_max_body_size directive. If this value is exceeded, Nginx will return a 413 Request Entity Too Large error. Step-by-Step Fix Locate the Nginx Configuration File Default location: /etc/nginx/nginx.conf For site-specific configurations: /etc/nginx/sites-available/ or /etc/nginx/conf.d/. Adjust the client_max_body_size Add or modify the directive in the appropriate http, server, or location block. Examples: Increase upload size globally: http { client_max_body_size 100M; # Set to 100 MB } Increase upload size for a specific site: server { server_name example.com; client_max_body_size 100M; } Increase upload size for a specific directory: location /uploads/ { client_max_body_size 100M; } Restart Nginx Apply the changes: sudo systemctl restart nginx Verify Changes Upload a file to test. Check logs for errors: /var/log/nginx/error.log. For Apache Apache restricts file uploads using the LimitRequestBody directive. If PHP is in use, it may also be restricted by post_max_size and upload_max_filesize. Step-by-Step Fix Locate the Apache Configuration File Default location: /etc/httpd/conf/httpd.conf (CentOS/Red Hat) or /etc/apache2/apache2.conf (Ubuntu/Debian). Virtual host configurations are often in /etc/httpd/sites-available/ or /etc/apache2/sites-available/. Adjust LimitRequestBody Modify or add the directive in the <Directory> or <VirtualHost> block. Increase upload size globally: <Directory "/var/www/html"> LimitRequestBody 104857600 # 100 MB </Directory> Increase upload size for a specific virtual host: <VirtualHost *:80> ServerName example.com DocumentRoot /var/www/example.com <Directory "/var/www/example.com"> LimitRequestBody 104857600 # 100 MB </Directory> </VirtualHost> Update PHP Settings (if applicable) Edit the php.ini file (often in /etc/php.ini or /etc/php/7.x/apache2/php.ini). Modify these values: upload_max_filesize = 100M post_max_size = 100M Restart Apache to apply changes: sudo systemctl restart apache2 # For Ubuntu/Debian sudo systemctl restart httpd # For CentOS/Red Hat Verify Changes Upload a file to test. Check logs: /var/log/apache2/error.log. Examples for Common Scenarios Allow Large File Uploads to a Specific Directory (Nginx): To allow uploads up to 200 MB in a directory /var/www/uploads/: location /uploads/ { client_max_body_size 200M; } Allow Large File Uploads for a Subdomain (Apache): For a subdomain uploads.example.com: <VirtualHost *:80> ServerName uploads.example.com DocumentRoot /var/www/uploads.example.com <Directory "/var/www/uploads.example.com"> LimitRequestBody 209715200 # 200 MB </Directory> </VirtualHost> Allow Large POST Requests (PHP Sites): Ensure PHP settings align with web server limits. For example, to allow 150 MB uploads: upload_max_filesize = 150M post_max_size = 150M max_execution_time = 300 # Allow enough time for the upload max_input_time = 300 Handling Large API Payloads (Nginx): If your API endpoint needs to handle JSON payloads up to 50 MB: location /api/ { client_max_body_size 50M; } General Best Practices Set Reasonable Limits: Avoid excessively high limits that might strain server resources. Optimize Server Resources: Use gzip or other compression techniques for file transfers. Monitor CPU and memory usage during large uploads. Secure Your Configuration: Only increase limits where necessary. Validate file uploads on the server-side to prevent abuse. Test Thoroughly: Use files of varying sizes to confirm functionality. Check server logs to troubleshoot unexpected issues.

You’re in a dark room with a candle, a wood stove, and a gas lamp. You only have one match. What do you light first? Hint: Sequence matters.

RHEL 8 (Red Hat Enterprise Linux) is a robust and secure operating system, but like any system, it can present challenges. Below, we explore ten common issues and provide actionable solutions with detailed explanations suitable for beginners. 1. Dependency Resolution Errors During Software Installation Problem: When using dnf or yum, you might encounter errors like: Error: Package dependency conflicts Cause: Missing or conflicting dependencies in the repository. Solution: Clear the DNF or YUM cache and retry: sudo dnf clean all sudo dnf update sudo dnf install <package> This ensures that outdated or corrupted cache files are removed, allowing the package manager to start fresh. Enable additional repositories if needed: If you don’t know the repository name, list available repositories: sudo subscription-manager repos --list Common repositories in RHEL include: rhel-8-for-x86_64-appstream-rpms for application streams. rhel-8-for-x86_64-baseos-rpms for the base operating system. Enable the repository with the following command: sudo subscription-manager repos --enable=<repo_name> This step adds the necessary repository where the required packages are stored. If the issue persists, check for alternative packages or versions: sudo dnf provides <missing_dependency> 2. Failed to Start GNOME Display Manager Problem: The graphical interface fails to load after boot. Cause: Misconfigured display settings, missing packages, or driver issues related to your GPU or video hardware. Solution: Check Logs for Clues: Logs provide detailed error messages to help pinpoint the issue. journalctl -xe | grep gdm journalctl -b | grep 'graphics' Look for errors related to the GNOME Display Manager (GDM) or graphics drivers. Reinstall or Install Missing GNOME Packages: If the GNOME display manager is not installed or corrupted, reinstall it: sudo dnf groupinstall "Server with GUI" sudo systemctl set-default graphical.target sudo systemctl restart gdm This installs the GNOME environment and ensures it starts by default. Verify and Update Graphics Drivers: If you're using dedicated GPU hardware (e.g., NVIDIA or AMD), ensure the drivers are correctly installed. For NVIDIA: sudo dnf install nvidia-driver sudo systemctl restart gdm For open-source drivers: sudo dnf install xorg-x11-drv-vesa xorg-x11-drv-evdev This ensures compatibility with your video hardware. Test Alternative Display Managers: If GDM fails to work, try an alternative display manager like LightDM: sudo dnf install lightdm sudo systemctl enable lightdm --force sudo systemctl start lightdm Fallback to Command Line for Recovery: If the graphical interface is entirely inaccessible, use TTY mode (Ctrl + Alt + F2) to log in and troubleshoot further: sudo systemctl set-default multi-user.target sudo systemctl restart gdm 3. SELinux Denying Legitimate Actions Problem: SELinux blocks actions with errors like: AVC denial: access denied Cause: SELinux policies are too restrictive for the action being performed. Solution: Check SELinux Logs: Use ausearch to identify what SELinux blocked: sudo ausearch -m avc -ts today This command shows detailed logs of blocked actions. Generate a Custom SELinux Policy: If SELinux is blocking a legitimate action, create a custom policy to allow it: sudo ausearch -c '<command>' --raw | audit2allow -M mypolicy sudo semodule -i mypolicy.pp Replace <command> with the blocked command to generate and apply the policy module. Temporarily Change SELinux Mode (Not Recommended for Production): For testing purposes, switch SELinux to permissive mode: sudo setenforce 0 This disables enforcement but logs violations. Don’t forget to revert back: sudo setenforce 1 4. Network Configuration Issues Problem: Network interface fails to connect. Cause: Incorrect or missing configuration in NetworkManager or physical hardware issues. Solution: Verify Connection Details: List active connections: sudo nmcli connection show If your desired connection isn’t active, bring it up manually: sudo nmcli connection up <connection_name> Restart Network Services: Sometimes restarting the network manager resolves transient issues: sudo systemctl restart NetworkManager Check IP Configuration: Verify if the interface has a valid IP address: ip addr show If not, troubleshoot the DHCP configuration or assign a static IP address. Test Connectivity: Use ping to check the connection: ping 8.8.8.8 If this works but domain names fail, investigate DNS settings. Inspect Hardware: Check the physical connection and ensure the network card is recognized: lspci | grep Ethernet 5. Kernel Panic on Boot Problem: System halts with a kernel panic, often accompanied by cryptic error messages. Cause: Corrupt kernel, incompatible kernel modules, or hardware issues. Solution: Boot into an Older Kernel: During boot, access the GRUB menu and select a previous kernel version. Reinstall the Kernel: If the kernel is corrupted, reinstall it: sudo dnf reinstall kernel Update GRUB Configuration: Ensure GRUB is properly configured to boot the updated kernel: sudo grub2-mkconfig -o /boot/grub2/grub.cfg Check Hardware: Run a memory and hardware test to ensure physical components aren’t failing. 6. Time Synchronization Issues Problem: System time is incorrect or out of sync. Cause: Misconfigured chronyd service or missing NTP servers. Solution: Verify chronyd Status: Check if the service is running: sudo systemctl status chronyd Sync Time Manually: Force a synchronization: sudo chronyc makestep Edit Configuration: Update /etc/chrony.conf with the correct NTP servers: server 0.centos.pool.ntp.org iburst server 1.centos.pool.ntp.org iburst Restart the Service: Apply changes by restarting the service: sudo systemctl restart chronyd 7. Filesystem Corruption Problem: System reports errors when accessing files or directories. Cause: Power failure or improper shutdown. Solution: Run fsck: Boot into single-user mode and repair the filesystem: sudo fsck -y /dev/<partition> Backup Critical Data: Always back up important files before attempting repairs. Use Journaled Filesystems: Ensure your partitions are using ext4 or another journaled filesystem to reduce future risks. 8. YUM/DNF Lock Error Problem: You see errors like: Another app is currently holding the yum lock Cause: Another process is using dnf or yum. Solution: Kill the Offending Process: Identify and terminate the process: sudo ps aux | grep dnf sudo kill -9 <PID> Remove Lock Files: Clear any lingering lock files: sudo rm -f /var/run/dnf.pid Retry the Operation: Restart your package manager command. 9. Service Fails to Start Problem: A service doesn’t start, with errors like: Job for <service>.service failed Cause: Misconfiguration, missing dependencies, or permission issues. Solution: Check Service Status: Review the service details: sudo systemctl status <service> Inspect Logs: Look for error messages: journalctl -xe Reconfigure the Service: Edit the service configuration files or reinstall the associated package: sudo dnf reinstall <package> Verify Dependencies: Ensure all required dependencies are installed. 10. Authentication Issues with SSH Problem: Cannot log in via SSH. Cause: Incorrect configuration in sshd_config or permission issues. Solution: Verify Configuration: Check the SSH configuration file: sudo nano /etc/ssh/sshd_config Ensure settings like PermitRootLogin and PasswordAuthentication are configured correctly. Restart SSH Service: Apply changes by restarting SSH: sudo systemctl restart sshd Correct File Permissions: Ensure proper permissions for the .ssh directory and files: chmod 700 ~/.ssh chmod 600 ~/.ssh/authorized_keys Test Connectivity: Use verbose mode to troubleshoot: ssh -vvv user@hostname By addressing these common RHEL 8 issues, you can maintain a stable and secure environment. Bookmark this guide for quick reference or share it on your forum to help others.

As I finish up the Blogger's account to auto post new Blogs for Linux, I am now starting the Facebook post implementation. Over the next few days, you may see posts in random categories that may disappear and reappear as I am testing.