🔒 Fix path traversal vulnerability in SaveVisualizationAsFile

[Dor-bl]

🎯 What: The SaveVisualizationAsFile method lacked validation on the user-supplied fileName, directly writing the Base64 visualization to the provided path.
⚠️ Risk: An attacker controlling the filename could provide an absolute path (C:\Windows\System32\malicious.dll) or use relative path traversal (../../etc/passwd) to overwrite arbitrary files on the local filesystem.
🛡️ Solution: The method now restricts the output file location to the application's current working directory. It uses Path.GetFullPath combined with StartsWith to ensure that no directory traversal sequences or absolute paths escape the allowed base directory. Invalid path characters are also sanitized.

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PR created automatically by Jules for task 2834004444876715981 started by @Dor-bl

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[Copilot]

Pull request overview

This PR hardens the image-comparison result API by preventing path traversal/absolute-path overwrites when saving the base64 visualization to disk.

Changes:

• Added argument validation for fileName before writing the visualization.
• Resolved the target path to a full path under the current working directory and blocked paths outside it.
• Updated file writing to use the validated full path.

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

fullPath.StartsWith(..., OrdinalIgnoreCase) can be bypassed on case-sensitive file systems (e.g., Linux/macOS) by traversing into a differently-cased sibling directory (e.g., ../App/... vs base .../app). Use an OS-appropriate comparison (Ordinal on non-Windows) or avoid string prefix checks altogether by using Path.GetRelativePath(baseDir, fullPath) and rejecting rooted/..-prefixed results.

Suggested change

	if (!allowedDirectory.EndsWith(Path.DirectorySeparatorChar.ToString()))
	{
	allowedDirectory += Path.DirectorySeparatorChar;
	}
	string fullPath = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), fileName));
	if (!fullPath.StartsWith(allowedDirectory, StringComparison.OrdinalIgnoreCase))
	string fullPath = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), fileName));
	string relativePath = Path.GetRelativePath(allowedDirectory, fullPath);
	if (Path.IsPathRooted(relativePath) ||
	relativePath.Equals("..", StringComparison.Ordinal) ||
	relativePath.StartsWith(".." + Path.DirectorySeparatorChar, StringComparison.Ordinal))

[Copilot]

This method throws ArgumentNullException for an empty string because it uses IsNullOrEmpty. Consider throwing ArgumentException for "" and reserving ArgumentNullException for null to match common .NET exception semantics for public APIs.

Suggested change

	if (string.IsNullOrEmpty(fileName))
	{
	throw new ArgumentNullException(nameof(fileName));
	}
	if (fileName is null)
	{
	throw new ArgumentNullException(nameof(fileName));
	}
	if (fileName.Length == 0)
	{
	throw new ArgumentException("The file name must not be an empty string.", nameof(fileName));
	}

[Copilot]

The PR description says invalid path characters are "sanitized", but the implementation rejects them by throwing. Either update the description to reflect the behavior or implement actual sanitization so callers get the promised behavior.

[Copilot]

Directory.GetCurrentDirectory() is called twice (for allowedDirectory and again when building fullPath). Capture the current directory once and reuse it to avoid inconsistent results if the working directory changes between calls (and to simplify the logic).

Suggested change

	string allowedDirectory = Path.GetFullPath(Directory.GetCurrentDirectory());
	if (!allowedDirectory.EndsWith(Path.DirectorySeparatorChar.ToString()))
	{
	allowedDirectory += Path.DirectorySeparatorChar;
	}
	string fullPath = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), fileName));
	string currentDirectory = Directory.GetCurrentDirectory();
	string allowedDirectory = Path.GetFullPath(currentDirectory);
	if (!allowedDirectory.EndsWith(Path.DirectorySeparatorChar.ToString()))
	{
	allowedDirectory += Path.DirectorySeparatorChar;
	}
	string fullPath = Path.GetFullPath(Path.Combine(currentDirectory, fileName));

[Copilot]

Restricting to a base directory via path-string checks does not prevent symlink traversal (e.g., saving to subdir/file.png where subdir is a symlink to an external location). If this API can be called with untrusted fileName and the base directory is writable by untrusted users, consider mitigating by detecting/rejecting symlinks along the path (where supported) or clearly documenting this limitation.

Suggested change

	File.WriteAllBytes(fullPath, Convert.FromBase64String(Visualization));
	}
	if (ContainsSymlinkWithinBaseDirectory(allowedDirectory, fullPath))
	{
	throw new IOException("The path to the output file traverses a symbolic link or reparse point, which is not allowed.");
	}
	File.WriteAllBytes(fullPath, Convert.FromBase64String(Visualization));
	}
	private static bool ContainsSymlinkWithinBaseDirectory(string allowedDirectory, string fullPath)
	{
	if (string.IsNullOrEmpty(allowedDirectory))
	{
	throw new ArgumentNullException(nameof(allowedDirectory));
	}
	if (string.IsNullOrEmpty(fullPath))
	{
	throw new ArgumentNullException(nameof(fullPath));
	}
	// Ensure the allowed directory has a trailing directory separator for reliable prefix checks.
	if (!allowedDirectory.EndsWith(Path.DirectorySeparatorChar.ToString()) &&
	!allowedDirectory.EndsWith(Path.AltDirectorySeparatorChar.ToString()))
	{
	allowedDirectory += Path.DirectorySeparatorChar;
	}
	// If the path is not under the allowed directory, treat it as unsafe.
	if (!fullPath.StartsWith(allowedDirectory, StringComparison.OrdinalIgnoreCase))
	{
	return true;
	}
	string relativePath = fullPath.Substring(allowedDirectory.Length);
	if (relativePath.Length == 0)
	{
	return false;
	}
	var separators = new[] { Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar };
	string[] parts = relativePath.Split(separators, StringSplitOptions.RemoveEmptyEntries);
	string currentPath = allowedDirectory.TrimEnd(separators);
	foreach (string part in parts)
	{
	currentPath = Path.Combine(currentPath, part);
	if (Directory.Exists(currentPath) || File.Exists(currentPath))
	{
	FileAttributes attributes;
	try
	{
	attributes = File.GetAttributes(currentPath);
	}
	catch (IOException)
	{
	// If attributes cannot be read, treat the path as unsafe.
	return true;
	}
	catch (UnauthorizedAccessException)
	{
	// If attributes cannot be read due to permissions, treat the path as unsafe.
	return true;
	}
	if ((attributes & FileAttributes.ReparsePoint) != 0)
	{
	// A reparse point (including symlinks/junctions) is present along the path.
	return true;
	}
	}
	}
	return false;
	}