security: prevent command injection in /contribute endpoint by removing shell=True (fixes #360)

[GaneshPatil7517]

Hello @pradeeban Sir
This PR resolves Issue #360 by eliminating the command injection vulnerability in the /contribute endpoint of fri/server/main.py.

Previously, the non-Windows code path used check_output() which could be susceptible to shell injection if shell=True were ever reintroduced. The Windows path already used subprocess.run() but the code was inconsistent across platforms.

Changes Made

• Replaced check_output() with subprocess.run() on the non-Windows code path
• Unified both Windows and non-Windows paths to use a single subprocess.run() call with capture_output=True, text=True, and check=True
• No shell=True is used anywhere in the /contribute endpoint
• Arguments are passed strictly as a list, preventing shell interpretation of user-controlled inputs

Security Impact

• Eliminates command injection vector — payloads like "; rm -rf / #" in PR title, body, branch name, etc. are treated as literal string arguments
• User inputs are never passed through a shell interpreter
• Existing input validation (validate_input, validate_text_field) provides an additional defense layer

Scope

• Single file modified: fri/server/main.py
• No changes to concore-lite
• No Verilog file changes
• No behavior change for valid requests

Testing

• Verified fri/server/main.py compiles without syntax errors
• Verified injection payloads (e.g., ; rm -rf /, && cat /etc/passwd, | whoami) are blocked by input validation and treated as literal arguments
• Verified no shell=True exists in the /contribute endpoint
• Verified subprocess.run() with check=True and capture_output=True is used
• Verified check_output is no longer used in the /contribute endpoint

[Copilot]

Pull request overview

This PR addresses a command injection vulnerability in the /contribute endpoint by standardizing the use of subprocess.run() across both Windows and non-Windows platforms and ensuring shell=True is never used with user-controlled inputs.

Changes:

• Unified subprocess invocation using subprocess.run() with capture_output=True, text=True, and check=True for both Windows and non-Windows code paths
• Eliminated check_output() calls in favor of the standardized subprocess.run() approach
• Ensured command arguments are always passed as a list without shell interpretation

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