security: implement pentest remediation (RATE-002, CLI-001)

RATE-002: Proactive rate limit cleanup when entries exceed threshold
- Add RATE_LIMIT_CLEANUP_THRESHOLD config (default 0.8)
- Trigger cleanup before hitting hard limit
- Prevents memory exhaustion under sustained load

CLI-001: Validate clipboard tool paths against trusted directories
- Add TRUSTED_CLIPBOARD_DIRS for Unix system paths
- Add TRUSTED_WINDOWS_PATTERNS for Windows validation
- Reject tools in user-writable locations (PATH hijack prevention)
- Use absolute paths in subprocess calls

tests/test_cli_security.py

@@ -0,0 +1,96 @@
+"""Tests for CLI security features (CLI-001: clipboard tool validation)."""
+
+import importlib.machinery
+import importlib.util
+import sys
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+
+def load_fpaste_module():
+    """Load the fpaste script as a module."""
+    fpaste_path = Path(__file__).parent.parent / "fpaste"
+    spec = importlib.util.spec_from_loader(
+        "fpaste",
+        importlib.machinery.SourceFileLoader("fpaste", str(fpaste_path)),
+    )
+    if spec is None or spec.loader is None:
+        pytest.skip("Could not load fpaste module")
+
+    fpaste = importlib.util.module_from_spec(spec)
+    sys.modules["fpaste"] = fpaste
+    spec.loader.exec_module(fpaste)
+    return fpaste
+
+
+class TestClipboardPathValidation:
+    """Tests for CLI-001: clipboard tool path validation."""
+
+    @pytest.fixture
+    def fpaste(self):
+        """Load fpaste module."""
+        return load_fpaste_module()
+
+    def test_trusted_unix_paths(self, fpaste):
+        """Paths in trusted Unix directories should be accepted."""
+        assert fpaste.is_trusted_clipboard_path("/usr/bin/xclip") is True
+        assert fpaste.is_trusted_clipboard_path("/usr/local/bin/xsel") is True
+        assert fpaste.is_trusted_clipboard_path("/bin/cat") is True
+        assert fpaste.is_trusted_clipboard_path("/opt/homebrew/bin/pbcopy") is True
+
+    def test_untrusted_unix_paths(self, fpaste):
+        """Paths in user-writable directories should be rejected."""
+        assert fpaste.is_trusted_clipboard_path("/home/user/bin/xclip") is False
+        assert fpaste.is_trusted_clipboard_path("/tmp/xclip") is False
+        assert fpaste.is_trusted_clipboard_path("/var/tmp/malicious") is False
+        assert fpaste.is_trusted_clipboard_path("./xclip") is False
+        assert fpaste.is_trusted_clipboard_path("") is False
+
+    def test_none_path_rejected(self, fpaste):
+        """None path should be rejected."""
+        # is_trusted_clipboard_path should handle None gracefully
+        assert fpaste.is_trusted_clipboard_path(None) is False
+
+    @pytest.mark.skipif(sys.platform != "win32", reason="Windows path tests only run on Windows")
+    def test_trusted_windows_paths(self, fpaste):
+        """Paths in trusted Windows directories should be accepted."""
+        # Test Windows paths (case-insensitive)
+        assert fpaste.is_trusted_clipboard_path("C:\\Windows\\System32\\clip.exe") is True
+        assert fpaste.is_trusted_clipboard_path("C:\\WINDOWS\\SYSTEM32\\clip.exe") is True
+        assert fpaste.is_trusted_clipboard_path("C:\\Program Files\\tool.exe") is True
+
+    def test_untrusted_windows_paths(self, fpaste):
+        """Paths in user-writable Windows directories should be rejected."""
+        assert fpaste.is_trusted_clipboard_path("C:\\Users\\user\\xclip.exe") is False
+        assert fpaste.is_trusted_clipboard_path("C:\\Temp\\malicious.exe") is False
+
+    def test_find_clipboard_command_rejects_untrusted(self, fpaste):
+        """find_clipboard_command should reject tools in untrusted paths."""
+        with patch("shutil.which") as mock_which:
+            # Untrusted path should be rejected
+            mock_which.return_value = "/tmp/malicious/xclip"
+            result = fpaste.find_clipboard_command(fpaste.CLIPBOARD_READ_COMMANDS)
+            assert result is None
+
+    def test_find_clipboard_command_accepts_trusted(self, fpaste):
+        """find_clipboard_command should accept tools in trusted paths."""
+        with patch("shutil.which") as mock_which:
+            # Trusted path should be accepted
+            mock_which.return_value = "/usr/bin/xclip"
+            result = fpaste.find_clipboard_command(fpaste.CLIPBOARD_READ_COMMANDS)
+            assert result is not None
+            assert result[0] == "/usr/bin/xclip"
+
+    def test_find_clipboard_uses_absolute_path(self, fpaste):
+        """find_clipboard_command should use absolute paths."""
+        with patch("shutil.which") as mock_which:
+            mock_which.return_value = "/usr/bin/xclip"
+            result = fpaste.find_clipboard_command(fpaste.CLIPBOARD_READ_COMMANDS)
+
+            # Should use absolute path, not just tool name
+            assert result[0] == "/usr/bin/xclip"
+            # Rest of command args should be preserved
+            assert "-selection" in result
+            assert "clipboard" in result