🛡️ Sentinel: [CRITICAL] Fix arbitrary code execution in excel cell writer

[inherent-vice]

🛡️ Sentinel: [CRITICAL] Fix arbitrary code execution in excel cell writer

🚨 Severity: CRITICAL
💡 Vulnerability: Command Injection / Arbitrary Code Execution. The write_excel_cell function dynamically generated a Python script using unsanitized string variables and ran it via subprocess.
🎯 Impact: An attacker who can control inputs like file path or cell value could escape string literals and execute arbitrary Python code on the host machine.
🔧 Fix: Constructed a static python script and passed the dynamic inputs securely via JSON over standard input (stdin) instead of relying on f-strings. Added correct exception handling and timeout processing.
✅ Verification: Ran pytest test suite. Verified code statically. Code review approved.

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PR created automatically by Jules for task 5159838291936685082 started by @agno7766

Summary by CodeRabbit

• Bug Fixes
  • Resolved a security vulnerability to prevent unauthorized code execution, ensuring safer and more reliable data handling across the application.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 74bd743a-8ca1-4525-8bf3-cab9b248b26f

📥 Commits

Reviewing files that changed from the base of the PR and between b18dfb2 and c069be0.

📒 Files selected for processing (2)

• .jules/sentinel.md
• CouponCheck/tui/data/providers.py

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📝 Walkthrough

Walkthrough

This PR prevents command injection in the Excel cell writer by replacing f-string interpolation with stdin JSON input passing. A vulnerability in write_excel_cell is documented in a new sentinel entry, and the implementation is refactored to use a static Python subprocess script that reads cell metadata from stdin instead of embedding variables directly in generated code.

Changes

Code injection prevention in Excel writer

Layer / File(s)	Summary
Vulnerability documentation .jules/sentinel.md	Sentinel entry documenting arbitrary code execution risk in the Excel cell writer, the dynamic code generation cause, and mitigation guidance to avoid f-string code generation and use safer input methods (JSON/stdin, argparse, environment variables).
Subprocess stdin-based input passing CouponCheck/tui/data/providers.py	write_excel_cell refactored to construct a static Python -c script with hardcoded logic, pass cell metadata (xlsm_path, sheet, cell, value) as JSON via stdin, use communicate(input=..., timeout=30) for explicit timeout handling, and return standardized event objects ({type: "exit", ...}, {type: "error", ...}) instead of embedding interpolated variables into the generated script string.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A script once whispered secrets through the shell,
'Til stdin's JSON made injection's spell break free,
No f-strings dance where data flows—just pure,
Tamed subprocess communion, timeout sure,
The hole is patched, the cells now safely true! 🔒✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly addresses the main change: fixing a critical arbitrary code execution vulnerability in the excel cell writer function through safer input handling.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch sentinel/fix-code-execution-5159838291936685082

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