gh-160782: reject line breaks in the venv directory and prompt

Lib/test/test_venv.py

@@ -1075,6 +1075,23 @@ def test_pathsep_error(self):
         self.assertRaises(ValueError, venv.create, bad_itempath)
         self.assertRaises(ValueError, venv.create, FakePath(bad_itempath))
 
+    def test_line_break_error(self):
+        """
+        Test that venv creation fails when the target directory or the
+        prompt contains a line break.
+        """
+        rmtree(self.env_dir)
+        for line_break in '\n', '\r':
+            with self.subTest(line_break=line_break):
+                bad_itempath = f'{self.env_dir}{line_break}x'
+                self.assertRaises(ValueError, venv.create, bad_itempath)
+                self.assertRaises(ValueError, venv.create,
+                                  FakePath(bad_itempath))
+                bad_prompt = f'x{line_break}x'
+                self.assertRaises(ValueError, venv.create, self.env_dir,
+                                  prompt=bad_prompt)
+                self.assertFalse(os.path.exists(self.env_dir))
+
     @unittest.skipIf(os.name == 'nt', 'not relevant on Windows')
     @requireVenvCreate
     def test_zippath_from_non_installed_posix(self):

Lib/venv/__init__.py

@@ -149,6 +149,13 @@ def create_if_needed(d):
         if os.pathsep in os.fspath(env_dir):
             raise ValueError(f'Refusing to create a venv in {env_dir} because '
                              f'it contains the PATH separator {os.pathsep}.')
+        if '\n' in os.fspath(env_dir) or '\r' in os.fspath(env_dir):
+            raise ValueError(f'Refusing to create a venv in {env_dir!r} '
+                             'because its path contains a line break.')
+        if self.prompt is not None and ('\n' in self.prompt
+                                        or '\r' in self.prompt):
+            raise ValueError(f'Refusing to use the prompt {self.prompt!r} '
+                             'because it contains a line break.')
         if os.path.exists(env_dir) and self.clear:
             self.clear_directory(env_dir)
         context = types.SimpleNamespace()

Misc/NEWS.d/next/Library/2026-10-30-09-59-22.gh-issue-160782.fN0HIu.rst

@@ -0,0 +1,2 @@
+:mod:`venv`: a line break in the prompt or the path now raises
+:exc:`ValueError` instead of being written into ``pyvenv.cfg``.