4 files changed, 40 insertions, 1 deletions
diff --git a/django/core/management/templates.py b/django/core/management/templates.py
index ea2c4a294f..1751f12cbc 100644
--- a/django/core/management/templates.py
+++ b/django/core/management/templates.py
@@ -18,6 +18,7 @@ from django.core.management.utils import (
 )
 from django.template import Context, Engine
 from django.utils import archive
+from django.utils._os import safe_join
 from django.utils.http import parse_header_parameters
 from django.utils.version import get_docs_version
 
@@ -345,7 +346,7 @@ class TemplateCommand(BaseCommand):
         # Move the temporary file to a filename that has better
         # chances of being recognized by the archive utils
         if used_name != guessed_filename:
-            guessed_path = os.path.join(tempdir, guessed_filename)
+            guessed_path = safe_join(tempdir, guessed_filename)
             shutil.move(the_path, guessed_path)
             return guessed_path
 
diff --git a/tests/admin_scripts/tests.py b/tests/admin_scripts/tests.py
index 819ba931d6..3eb7b97c99 100644
--- a/tests/admin_scripts/tests.py
+++ b/tests/admin_scripts/tests.py
@@ -2778,6 +2778,21 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         self.assertTrue(os.path.isdir(testproject_dir))
         self.assertTrue(os.path.exists(os.path.join(testproject_dir, "run.py")))
 
+    def test_custom_project_template_from_tarball_by_url_bad_filename(self):
+        """
+        The startproject management command will raise SuspiciousFileOperation
+        on an ill-formed remote template archive filename.
+        """
+        template_url = "%s/bad_template_filename.tgz" % self.live_server_url
+
+        args = ["startproject", "--template", template_url, "urltestproject"]
+
+        out, err = self.run_django_admin(args)
+        self.assertOutput(
+            err,
+            "is located outside of the base path component",
+        )
+
     def test_custom_project_template_from_tarball_by_url_django_user_agent(self):
         user_agent = None
 
diff --git a/tests/admin_scripts/urls.py b/tests/admin_scripts/urls.py
index a6cc7fe1b5..3e7aa063d3 100644
--- a/tests/admin_scripts/urls.py
+++ b/tests/admin_scripts/urls.py
@@ -3,6 +3,8 @@ import os
 from django.urls import path
 from django.views.static import serve
 
+from . import views
+
 here = os.path.dirname(__file__)
 
 urlpatterns = [
@@ -11,4 +13,8 @@ urlpatterns = [
         serve,
         {"document_root": os.path.join(here, "custom_templates")},
     ),
+    path(
+        "bad_template_filename.tgz",
+        views.template_bad_filename,
+    ),
 ]
diff --git a/tests/admin_scripts/views.py b/tests/admin_scripts/views.py
new file mode 100644
index 0000000000..d57803659d
--- /dev/null
+++ b/tests/admin_scripts/views.py
@@ -0,0 +1,17 @@
+from pathlib import Path
+
+from django.http import FileResponse
+
+
+def template_bad_filename(request):
+    content = Path(__file__).parent / "custom_templates" / "project_template.tgz"
+    f = open(content, "rb")
+    filename = "/nonexistent/archive.tgz"
+    response = FileResponse(
+        f,
+        as_attachment=True,
+        filename=filename,
+    )
+    # Force the filename to have a slash at the beginning.
+    response["Content-Disposition"] = f'attachment; filename="{filename}"'
+    return response