05/24 Fix Security bugs

routes/ai_summary.py

@@ -111,9 +111,41 @@ def analyze():
                    "file_count": len(file_names), **result})
 
 
+# Magic-byte signatures for each supported binary format.
+# Office Open XML (docx/xlsx) and legacy OLE (doc/xls) share these headers.
+_FILE_MAGIC: dict = {
+    ".pdf":  b"%PDF",
+    ".docx": b"PK\x03\x04",
+    ".xlsx": b"PK\x03\x04",
+    ".doc":  b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1",
+    ".xls":  b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1",
+}
+
+
+def _validate_magic(data: bytes, ext: str) -> None:
+    """Raise ValueError if the file's actual bytes don't match its extension."""
+    magic = _FILE_MAGIC.get(ext)
+    if magic:
+        if data[: len(magic)] != magic:
+            raise ValueError(
+                f"File content does not match the declared {ext} format "
+                "(possible disguised upload)."
+            )
+    elif ext in (".txt", ".csv", ".md"):
+        # Text files must be decodable; binary data masquerading as text is rejected.
+        try:
+            data[:512].decode("utf-8")
+        except UnicodeDecodeError:
+            raise ValueError(
+                "Text file does not appear to be valid UTF-8. "
+                "Ensure the file is a plain text document."
+            )
+
+
 def _extract_text(file_obj, ext: str) -> str:
     """Extract plain text from an uploaded file object."""
     data = file_obj.read()
+    _validate_magic(data, ext)
 
     if ext in (".txt", ".md", ".csv"):
         return data.decode("utf-8", errors="replace")