🛡️ Sentinel: [CRITICAL] Fix command injection vulnerability

[ManupaKDU]

• 🚨 Severity: CRITICAL
• 💡 Vulnerability: Command injection vulnerability in the is_reachable function of testping1.py. The ip parameter was passed directly to subprocess.Popen without any validation or sanitization, allowing an attacker to execute arbitrary system commands if they could control the input (e.g., providing an IP like "192.168.1.1; rm -rf /").
• 🎯 Impact: If exploited, an attacker could achieve arbitrary code execution on the system running the network scanner, potentially compromising the host machine entirely.
• 🔧 Fix: Introduced strict input validation using Python's built-in ipaddress.ip_address() function. The function now ensures that the provided input is a structurally valid IPv4 or IPv6 address before attempting to execute the ping command. Malformed or malicious inputs will safely raise a ValueError and return False. Accompanying unit tests were added to ensure this functionality works as intended and doesn't trigger the subprocess call for invalid IPs.
• ✅ Verification: Run python3 -m unittest test_testping1.py to verify the tests pass. The new test_is_reachable_invalid_ip test explicitly checks that invalid and malicious input correctly returns False without executing system commands.

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PR created automatically by Jules for task 13666445682335031747 started by @ManupaKDU

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