diff --git a/tests/tools/test_green_screen_chromakey.py b/tests/tools/test_green_screen_chromakey.py
index ab4bcf3a7f..6d1743cfc9 100644
--- a/tests/tools/test_green_screen_chromakey.py
+++ b/tests/tools/test_green_screen_chromakey.py
@@ -114,3 +114,56 @@ def _pixel(p, x, y):
     corner = _pixel(out, 10, 10)     # was green -> keyed to dark background
     assert center[0] > 150 and center[1] < 80, f"subject lost, center={center!r}"
     assert corner[0] < 60 and corner[1] < 60, f"green not keyed, corner={corner!r}"
+
+
+@pytest.mark.parametrize(
+    "invalid_color",
+    [
+        "#000000,drawbox=x=0:y=0:w=10:h=10:color=red",
+        "0x00FF00:size=1x1",
+        "red",
+        "black",
+        "00112",
+        "#1234567",
+        "invalid_hex",
+        "; rm -rf /",
+        "#00FF00[fg];",
+    ],
+)
+def test_validate_hex_color_rejects_malformed_and_injections(invalid_color):
+    tool = GreenScreenProcessor()
+    with pytest.raises(ValueError, match="Invalid bg_color"):
+        tool._validate_hex_color(invalid_color)
+
+
+@pytest.mark.parametrize(
+    ("valid_color", "expected_hex"),
+    [
+        ("#0E172A", "0E172A"),
+        ("0E172A", "0E172A"),
+        ("#00ff00", "00FF00"),
+        ("#fff", "FFFFFF"),
+        ("000", "000000"),
+        ("#0E172AFF", "0E172AFF"),
+    ],
+)
+def test_validate_hex_color_normalizes_valid_hex(valid_color, expected_hex):
+    tool = GreenScreenProcessor()
+    assert tool._validate_hex_color(valid_color) == expected_hex
+
+
+def test_execute_rejects_invalid_bg_color(tmp_path):
+    input_file = tmp_path / "input.mp4"
+    input_file.write_bytes(b"dummy")
+    output_file = tmp_path / "output.mp4"
+
+    tool = GreenScreenProcessor()
+    result = tool.execute(
+        {
+            "input_path": str(input_file),
+            "output_path": str(output_file),
+            "bg_color": "#000000,drawbox=color=red",
+        }
+    )
+    assert not result.success
+    assert "Invalid bg_color" in result.error
diff --git a/tools/video/green_screen_processor.py b/tools/video/green_screen_processor.py
index fdc9b7bf8d..352734f202 100644
--- a/tools/video/green_screen_processor.py
+++ b/tools/video/green_screen_processor.py
@@ -15,6 +15,7 @@
 import json
 import os
 import platform
+import re
 import shutil
 import time
 from pathlib import Path
@@ -121,7 +122,12 @@ def execute(self, inputs: dict[str, Any]) -> ToolResult:
 
         method = inputs.get("method", "auto")
         fps = inputs.get("fps", 15)
-        bg_color = inputs.get("bg_color", "#0E172A")
+        bg_color_raw = inputs.get("bg_color", "#0E172A")
+        try:
+            bg_hex = self._validate_hex_color(bg_color_raw)
+            bg_color = f"#{bg_hex}"
+        except ValueError as e:
+            return ToolResult(success=False, error=str(e))
         max_frames = inputs.get("max_frames", 0)
         start = time.time()
 
@@ -452,7 +458,7 @@ def _process_chromakey(
 
         Applies chromakey to remove green, then composites onto bg_color.
         """
-        bg_hex = bg_color.lstrip("#")
+        bg_hex = self._validate_hex_color(bg_color)
         # Convert hex to FFmpeg color format
         ffmpeg_bg = f"0x{bg_hex}"
 
@@ -542,7 +548,7 @@ def _process_rembg(
             return False
 
         # Parse bg_color hex to RGB
-        bg_hex = bg_color.lstrip("#")
+        bg_hex = self._validate_hex_color(bg_color)
         bg_r = int(bg_hex[0:2], 16)
         bg_g = int(bg_hex[2:4], 16)
         bg_b = int(bg_hex[4:6], 16)
@@ -605,6 +611,34 @@ def _reconstruct_video(
         ]
         self.run_command(cmd, timeout=600)
 
+    @staticmethod
+    def _validate_hex_color(bg_color: str) -> str:
+        """Validate and normalize a background hex color string.
+
+        Accepts 3, 6, or 8 character hex strings with optional leading "#".
+        Returns a canonical normalized uppercase hex string (e.g., "0E172A").
+        Raises ValueError if the input is not a valid hex color or contains
+        any injection characters.
+        """
+        if not isinstance(bg_color, str):
+            raise ValueError(f"Invalid bg_color: expected string, got {type(bg_color).__name__}")
+
+        s = bg_color.strip().removeprefix("#")
+
+        if not re.fullmatch(r"[0-9a-fA-F]+", s):
+            raise ValueError(
+                f"Invalid bg_color: '{bg_color}'. Expected hex color string (e.g., '#0E172A')."
+            )
+
+        if len(s) == 3:
+            return "".join(c * 2 for c in s).upper()
+        elif len(s) in (6, 8):
+            return s.upper()
+        else:
+            raise ValueError(
+                f"Invalid bg_color: '{bg_color}'. Expected 3, 6, or 8 hex digits."
+            )
+
     @staticmethod
     def _cleanup_dir(dir_path: Path) -> None:
         """Recursively remove a temp directory."""