🛡️ Sentinel: [CRITICAL] Fix path traversal in file_browser.py

[thirdeyenation]

🚨 Severity: CRITICAL

💡 Vulnerability: Path traversal in helpers.file_browser.py. Several methods (save_file_b64, save_files, delete_file, rename_item, create_folder, save_text_file, get_files) validated directory containment using a string-based check: str(target_path).startswith(str(self.base_dir)).

🎯 Impact: An attacker could craft paths like /app-secrets to bypass the containment check when base_dir is /app, allowing unauthorized read/write access to arbitrary files outside the designated directory structure, leading to potential data exposure or system compromise.

🔧 Fix: Replaced all vulnerable string startswith() checks with is_relative_to(self.base_dir) on the pathlib.Path objects to guarantee secure, true path containment validation.

✅ Verification: Verified by attempting directory escapes (e.g., passing paths traversing up to parallel directories) which are now successfully caught and blocked by the is_relative_to() check. Tests pass.

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PR created automatically by Jules for task 11436430875818666657 started by @thirdeyenation

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