FIX: validate UnicodeSubstitution start value (#2559)

Co-authored-by: Roman Lutz <romanlutz13@gmail.com>

Author: sylvesterkaczmarek

pyrit/converter/unicode_sub_converter.py

@@ -20,7 +20,12 @@ def __init__(self, *, start_value: int = 0xE0000) -> None:
 
         Args:
             start_value (int): The unicode starting point to use for encoding.
+
+        Raises:
+            ValueError: If ``start_value`` is outside the Unicode code point range.
         """
+        if not 0 <= start_value <= 0x10FFFF:
+            raise ValueError("start_value must be a valid Unicode code point between 0 and 0x10FFFF")
         self.startValue = start_value
 
     def _build_identifier(self) -> ComponentIdentifier:

tests/unit/converter/test_unicode_sub_converter.py

@@ -22,6 +22,12 @@ async def test_unicode_sub_custom_start():
     assert result.output_type == "text"
 
 
+@pytest.mark.parametrize("start_value", [-1, 0x110000])
+def test_unicode_sub_rejects_invalid_start_value(start_value):
+    with pytest.raises(ValueError, match="valid Unicode code point"):
+        UnicodeSubstitutionConverter(start_value=start_value)
+
+
 async def test_unicode_sub_empty():
     converter = UnicodeSubstitutionConverter()
     result = await converter.convert_async(prompt="", input_type="text")