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Introduction:
In the ever-evolving landscape of cybersecurity, theoretical knowledge is insufficient without practical, hands-on command-line expertise. This article provides a critical arsenal of verified commands for Linux, Windows, and security tools, enabling professionals to actively defend, audit, and harden their systems against modern threats.
Learning Objectives:
- Acquire proficiency in system reconnaissance, network monitoring, and vulnerability assessment using native command-line tools.
- Understand and implement critical security hardening techniques for both Linux and Windows environments.
- Develop the ability to analyze processes, manage incidents, and secure cloud and API endpoints from the terminal.
You Should Know:
1. System Reconnaissance and Enumeration
Before an attacker can exploit a system, they first seek to understand it. The following commands are fundamental for both penetration testing and defensive auditing.
`uname -a` (Linux): Displays all system information including kernel version, which is crucial for identifying potential kernel-level vulnerabilities.
`systeminfo` (Windows): Provides a comprehensive overview of the Windows system, including OS configuration, hotfixes, and installed patches.
`cat /etc/passwd` (Linux): Lists all users on the system. Defenders should audit this for unauthorized accounts.
`net user` & `net localgroup administrators` (Windows): Enumerates local users and members of the administrators group.
`ps aux –sort=-%mem` (Linux): Shows all running processes sorted by memory usage, helping to identify resource-hungry or malicious software.
Step-by-step guide: Start your audit by running `systeminfo` on Windows or `uname -a` on Linux. This gives you the baseline. Then, enumerate users with `net user` or by examining /etc/passwd. Finally, analyze running processes to establish a baseline of normal activity. Unfamiliar processes should be investigated immediately.
2. Network Security and Connection Monitoring
Visibility into network traffic is the cornerstone of detecting data exfiltration and unauthorized connections.
`netstat -tulnpe` (Linux): Lists all listening ports, the associated processes (PID/Program name), and user IDs. The `-e` switch adds extended information.
`Get-NetTCPConnection -State Listen` (Windows PowerShell): The PowerShell equivalent for displaying listening TCP ports.
`ss -tuln` (Linux): A faster, modern replacement for netstat.
`netsh advfirewall show allprofiles` (Windows): Displays the current configuration and status of the Windows Defender Firewall.
`tcpdump -i eth0 -w capture.pcap` (Linux): A powerful packet analyzer that captures raw traffic on interface `eth0` to a file for later analysis.
Step-by-step guide: To quickly audit network services, use `netstat -tulnpe` on Linux. Look for services listening on unexpected ports or running under unusual user accounts. On Windows, use `Get-NetTCPConnection` to achieve a similar result. For deep packet inspection, `tcpdump` is indispensable for capturing traffic that can be analyzed with tools like Wireshark.
3. File System Integrity and Log Auditing
Attackers often leave traces in logs and manipulate files. Knowing how to find these artifacts is critical.
`find / -perm -4000 2>/dev/null` (Linux): Finds all SUID binaries, which are a common privilege escalation vector.
`ls -la /etc/passwd` (Linux): Checks the permissions on the critical user database file. It should not be world-writable.
`Get-Acl C:\Windows\System32\config\SAM | Format-List` (Windows PowerShell): Checks permissions on the Windows SAM database file.
`sudo tail -f /var/log/auth.log` (Linux): Monitors the authentication log in real-time for login attempts (useful for detecting brute-force attacks).
`Get-WinEvent -FilterHashtable @{LogName=’Security’; ID=4625}` (Windows PowerShell): Filters the Security log for failed login events (Event ID 4625).
Step-by-step guide: Regularly search for SUID files with the `find` command and investigate any that are non-standard. Monitor your authentication logs in real-time during suspicious activity using tail -f. In Windows, script a PowerShell command to periodically pull failed login attempts to identify brute-force campaigns.
4. Vulnerability Scanning and Service Interrogation
Proactive discovery of weaknesses prevents exploitation.
`nmap -sV -sC -O
`nmap –script vuln
`Test-NetConnection -ComputerName
`nikto -h
`sqlmap -u “http://test.com/page.php?id=1″` (Linux): An automated tool for detecting and exploiting SQL injection flaws.
Step-by-step guide: Begin external assessments with an `nmap -sV -sC` scan to map the attack surface. For any web services discovered, run a `nikto` scan to identify common web server misconfigurations and vulnerabilities. Use `sqlmap` specifically on any input fields or URL parameters that may be susceptible to SQLi.
5. Incident Response and Process Management
When a breach is suspected, rapid and precise action is required.
`lsof -i :
`kill -9
`Get-Process | Where-Object {$_.CPU -gt 50}` (Windows PowerShell): Finds processes using more than 50% of CPU.
`Stop-Process -Name “malicious_process” -Force` (Windows PowerShell): Stops a process by its name.
`chkconfig –list | grep 3:on` (Linux – SysV) / `systemctl list-unit-files –type=service | grep enabled` (Linux – systemd): Lists all services that start automatically at boot.
Step-by-step guide: If a suspicious port is found with netstat, use `lsof -i :
6. Cloud and API Security Hardening
Security extends into the cloud, where misconfigurations are a primary threat.
`aws iam get-account-authorization-details` (AWS CLI): Retrieves IAM role, user, and policy details to audit for excessive permissions.
`az ad user list –query “[].{userPrincipalName:userPrincipalName, accountEnabled:accountEnabled}”` (Azure CLI): Lists Azure AD users and their status.
`gcloud projects get-iam-policy
Using `curl` for API Security Testing:
`curl -H “Authorization: Bearer
`curl -X POST https://api.example.com/login -d ‘{“user”:”admin”,”pass”:”password”}’ -H “Content-Type: application/json”` (Tests login endpoint).
Step-by-step guide: Regularly run the `aws iam get-account-authorization-details` command and use the AWS IAM policy simulator to validate that permissions adhere to the principle of least privilege. For APIs, use `curl` to script authentication tests and payload fuzzing, checking for error messages that reveal too much information.
7. Cryptography and Data Integrity Checks
Verifying the integrity and security of data and communications is non-negotiable.
`openssl s_client -connect example.com:443` (Linux): Tests and displays the SSL/TLS certificate chain and connection details for a remote server.
`sha256sum
`gpg –encrypt –recipient [email protected] file.txt` (Linux): Encrypts a file using GPG.
`certutil -hashfile
Step-by-step guide: Before deploying software or scripts, always verify their checksum. Download the published SHA256 sum from the official source and compare it to the output of sha256sum <downloaded_file>. For web servers, use `openssl s_client` to confirm that certificates are valid and that strong ciphers are being used.
What Undercode Say:
- The Command Line is the First and Last Line of Defense. Automation and scripting built on these commands are what separate proactive security teams from reactive ones.
- Visibility Equals Control. Without continuous enumeration, monitoring, and logging, an organization is operating blind to both threats and its own security posture.
The provided LinkedIn post, while highlighting a job role, underscores a critical industry truth: the demand for skilled engineers who possess deep, practical system expertise is relentless. The commands detailed here form the foundational lexicon for these roles. In cybersecurity, an attacker only needs to find one misconfigured service or one weak credential. The defender’s role is to eliminate all such possibilities. Mastery of this toolkit is not just about knowing the commands, but about developing the analytical mindset to interpret their output and take decisive, informed action. This practical skillset is what makes an IT professional truly invaluable in the current threat landscape.
Prediction:
The increasing complexity of hybrid cloud environments and the pervasive use of APIs will shift the focus of cyber attacks towards automation and configuration exploitation. Defenders who cannot script and orchestrate their security responses using command-line tools and APIs will be overwhelmed. The future belongs to security professionals who can codify their defense strategies, making them as scalable and agile as the attacks they aim to thwart.
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Julien Louis – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
