diff --git a/api/factories/file_factory.py b/api/factories/file_factory.py
index 2316e45179..737a79f2b0 100644
--- a/api/factories/file_factory.py
+++ b/api/factories/file_factory.py
@@ -1,5 +1,6 @@
 import mimetypes
 import os
+import re
 import urllib.parse
 import uuid
 from collections.abc import Callable, Mapping, Sequence
@@ -268,15 +269,47 @@ def _build_from_remote_url(
 
 
 def _extract_filename(url_path: str, content_disposition: str | None) -> str | None:
-    filename = None
+    filename: str | None = None
     # Try to extract from Content-Disposition header first
     if content_disposition:
-        _, params = parse_options_header(content_disposition)
-        # RFC 5987 https://datatracker.ietf.org/doc/html/rfc5987: filename* takes precedence over filename
-        filename = params.get("filename*") or params.get("filename")
+        # Manually extract filename* parameter since parse_options_header doesn't support it
+        filename_star_match = re.search(r"filename\*=([^;]+)", content_disposition)
+        if filename_star_match:
+            raw_star = filename_star_match.group(1).strip()
+            # Remove trailing quotes if present
+            raw_star = raw_star.removesuffix('"')
+            # format: charset'lang'value
+            try:
+                parts = raw_star.split("'", 2)
+                charset = (parts[0] or "utf-8").lower() if len(parts) >= 1 else "utf-8"
+                value = parts[2] if len(parts) == 3 else parts[-1]
+                filename = urllib.parse.unquote(value, encoding=charset, errors="replace")
+            except Exception:
+                # Fallback: try to extract value after the last single quote
+                if "''" in raw_star:
+                    filename = urllib.parse.unquote(raw_star.split("''")[-1])
+                else:
+                    filename = urllib.parse.unquote(raw_star)
+
+        if not filename:
+            # Fallback to regular filename parameter
+            _, params = parse_options_header(content_disposition)
+            raw = params.get("filename")
+            if raw:
+                # Strip surrounding quotes and percent-decode if present
+                if len(raw) >= 2 and raw[0] == raw[-1] == '"':
+                    raw = raw[1:-1]
+                filename = urllib.parse.unquote(raw)
     # Fallback to URL path if no filename from header
     if not filename:
-        filename = os.path.basename(url_path)
+        candidate = os.path.basename(url_path)
+        filename = urllib.parse.unquote(candidate) if candidate else None
+    # Defense-in-depth: ensure basename only
+    if filename:
+        filename = os.path.basename(filename)
+        # Return None if filename is empty or only whitespace
+        if not filename or not filename.strip():
+            filename = None
     return filename or None
 
 
diff --git a/api/tests/unit_tests/factories/test_file_factory.py b/api/tests/unit_tests/factories/test_file_factory.py
index 777fe5a6e7..e5f45044fa 100644
--- a/api/tests/unit_tests/factories/test_file_factory.py
+++ b/api/tests/unit_tests/factories/test_file_factory.py
@@ -2,7 +2,7 @@ import re
 
 import pytest
 
-from factories.file_factory import _get_remote_file_info
+from factories.file_factory import _extract_filename, _get_remote_file_info
 
 
 class _FakeResponse:
@@ -113,3 +113,120 @@ class TestGetRemoteFileInfo:
         # Should generate a random hex filename with .bin extension
         assert re.match(r"^[0-9a-f]{32}\.bin$", filename) is not None
         assert mime_type == "application/octet-stream"
+
+
+class TestExtractFilename:
+    """Tests for _extract_filename function focusing on RFC5987 parsing and security."""
+
+    def test_no_content_disposition_uses_url_basename(self):
+        """Test that URL basename is used when no Content-Disposition header."""
+        result = _extract_filename("http://example.com/path/file.txt", None)
+        assert result == "file.txt"
+
+    def test_no_content_disposition_with_percent_encoded_url(self):
+        """Test that percent-encoded URL basename is decoded."""
+        result = _extract_filename("http://example.com/path/file%20name.txt", None)
+        assert result == "file name.txt"
+
+    def test_no_content_disposition_empty_url_path(self):
+        """Test that empty URL path returns None."""
+        result = _extract_filename("http://example.com/", None)
+        assert result is None
+
+    def test_simple_filename_header(self):
+        """Test basic filename extraction from Content-Disposition."""
+        result = _extract_filename("http://example.com/", 'attachment; filename="test.txt"')
+        assert result == "test.txt"
+
+    def test_quoted_filename_with_spaces(self):
+        """Test filename with spaces in quotes."""
+        result = _extract_filename("http://example.com/", 'attachment; filename="my file.txt"')
+        assert result == "my file.txt"
+
+    def test_unquoted_filename(self):
+        """Test unquoted filename."""
+        result = _extract_filename("http://example.com/", "attachment; filename=test.txt")
+        assert result == "test.txt"
+
+    def test_percent_encoded_filename(self):
+        """Test percent-encoded filename."""
+        result = _extract_filename("http://example.com/", 'attachment; filename="file%20name.txt"')
+        assert result == "file name.txt"
+
+    def test_rfc5987_filename_star_utf8(self):
+        """Test RFC5987 filename* with UTF-8 encoding."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=UTF-8''file%20name.txt")
+        assert result == "file name.txt"
+
+    def test_rfc5987_filename_star_chinese(self):
+        """Test RFC5987 filename* with Chinese characters."""
+        result = _extract_filename(
+            "http://example.com/", "attachment; filename*=UTF-8''%E6%B5%8B%E8%AF%95%E6%96%87%E4%BB%B6.txt"
+        )
+        assert result == "测试文件.txt"
+
+    def test_rfc5987_filename_star_with_language(self):
+        """Test RFC5987 filename* with language tag."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=UTF-8'en'file%20name.txt")
+        assert result == "file name.txt"
+
+    def test_rfc5987_filename_star_fallback_charset(self):
+        """Test RFC5987 filename* with fallback charset."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=''file%20name.txt")
+        assert result == "file name.txt"
+
+    def test_rfc5987_filename_star_malformed_fallback(self):
+        """Test RFC5987 filename* with malformed format falls back to simple unquote."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=malformed%20filename.txt")
+        assert result == "malformed filename.txt"
+
+    def test_filename_star_takes_precedence_over_filename(self):
+        """Test that filename* takes precedence over filename."""
+        test_string = 'attachment; filename="old.txt"; filename*=UTF-8\'\'new.txt"'
+        result = _extract_filename("http://example.com/", test_string)
+        assert result == "new.txt"
+
+    def test_path_injection_protection(self):
+        """Test that path injection attempts are blocked by os.path.basename."""
+        result = _extract_filename("http://example.com/", 'attachment; filename="../../../etc/passwd"')
+        assert result == "passwd"
+
+    def test_path_injection_protection_rfc5987(self):
+        """Test that path injection attempts in RFC5987 are blocked."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=UTF-8''..%2F..%2F..%2Fetc%2Fpasswd")
+        assert result == "passwd"
+
+    def test_empty_filename_returns_none(self):
+        """Test that empty filename returns None."""
+        result = _extract_filename("http://example.com/", 'attachment; filename=""')
+        assert result is None
+
+    def test_whitespace_only_filename_returns_none(self):
+        """Test that whitespace-only filename returns None."""
+        result = _extract_filename("http://example.com/", 'attachment; filename="   "')
+        assert result is None
+
+    def test_complex_rfc5987_encoding(self):
+        """Test complex RFC5987 encoding with special characters."""
+        result = _extract_filename(
+            "http://example.com/",
+            "attachment; filename*=UTF-8''%E4%B8%AD%E6%96%87%E6%96%87%E4%BB%B6%20%28%E5%89%AF%E6%9C%AC%29.pdf",
+        )
+        assert result == "中文文件 (副本).pdf"
+
+    def test_iso8859_1_encoding(self):
+        """Test ISO-8859-1 encoding in RFC5987."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=ISO-8859-1''file%20name.txt")
+        assert result == "file name.txt"
+
+    def test_encoding_error_fallback(self):
+        """Test that encoding errors fall back to safe ASCII filename."""
+        result = _extract_filename("http://example.com/", "attachment; filename*=INVALID-CHARSET''file%20name.txt")
+        assert result == "file name.txt"
+
+    def test_mixed_quotes_and_encoding(self):
+        """Test filename with mixed quotes and percent encoding."""
+        result = _extract_filename(
+            "http://example.com/", 'attachment; filename="file%20with%20quotes%20%26%20encoding.txt"'
+        )
+        assert result == "file with quotes & encoding.txt"