diff --git a/HISTORY.md b/HISTORY.md
index edef710f0..50f855ba8 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -2,6 +2,8 @@
 
 History is important, but our current roadmap can be found [here](https://github.com/cookiecutter/cookiecutter/projects)
 
+## 2.1.1 (unreleased)
+
 ## 2.1.0 (2022-05-30)
 
 ### Changes
diff --git a/cookiecutter/vcs.py b/cookiecutter/vcs.py
index 08cb2eb0c..bb4356b31 100644
--- a/cookiecutter/vcs.py
+++ b/cookiecutter/vcs.py
@@ -98,8 +98,12 @@ def clone(repo_url, checkout=None, clone_to_dir='.', no_input=False):
                 stderr=subprocess.STDOUT,
             )
             if checkout is not None:
+                checkout_params = [checkout]
+                # Avoid Mercurial "--config" and "--debugger" injection vulnerability
+                if repo_type == "hg":
+                    checkout_params.insert(0, "--")
                 subprocess.check_output(  # nosec
-                    [repo_type, 'checkout', checkout],
+                    [repo_type, 'checkout', *checkout_params],
                     cwd=repo_dir,
                     stderr=subprocess.STDOUT,
                 )
@@ -107,13 +111,13 @@ def clone(repo_url, checkout=None, clone_to_dir='.', no_input=False):
             output = clone_error.output.decode('utf-8')
             if 'not found' in output.lower():
                 raise RepositoryNotFound(
-                    'The repository {} could not be found, '
-                    'have you made a typo?'.format(repo_url)
+                    f'The repository {repo_url} could not be found, '
+                    'have you made a typo?'
                 )
             if any(error in output for error in BRANCH_ERRORS):
                 raise RepositoryCloneFailed(
-                    'The {} branch of repository {} could not found, '
-                    'have you made a typo?'.format(checkout, repo_url)
+                    f'The {checkout} branch of repository '
+                    f'{repo_url} could not found, have you made a typo?'
                 )
             logger.error('git clone failed with error: %s', output)
             raise
diff --git a/tests/vcs/test_clone.py b/tests/vcs/test_clone.py
index 9fc3b24fa..bd19ef1ab 100644
--- a/tests/vcs/test_clone.py
+++ b/tests/vcs/test_clone.py
@@ -122,8 +122,16 @@ def test_clone_should_invoke_vcs_command(
     mock_subprocess.assert_any_call(
         [repo_type, 'clone', repo_url], cwd=str(clone_dir), stderr=subprocess.STDOUT
     )
+
+    branch_info = [branch]
+    # We sanitize branch information for Mercurial
+    if repo_type == "hg":
+        branch_info.insert(0, "--")
+
     mock_subprocess.assert_any_call(
-        [repo_type, 'checkout', branch], cwd=expected_repo_dir, stderr=subprocess.STDOUT
+        [repo_type, 'checkout', *branch_info],
+        cwd=expected_repo_dir,
+        stderr=subprocess.STDOUT,
     )
 
 
@@ -151,8 +159,8 @@ def test_clone_handles_repo_typo(mocker, clone_dir, error_message):
         vcs.clone(repository_url, clone_to_dir=str(clone_dir), no_input=True)
 
     assert str(err.value) == (
-        'The repository {} could not be found, have you made a typo?'
-    ).format(repository_url)
+        f'The repository {repository_url} could not be found, have you made a typo?'
+    )
 
 
 @pytest.mark.parametrize(
@@ -182,8 +190,8 @@ def test_clone_handles_branch_typo(mocker, clone_dir, error_message):
 
     assert str(err.value) == (
         'The unknown_branch branch of repository '
-        '{} could not found, have you made a typo?'
-    ).format(repository_url)
+        f'{repository_url} could not found, have you made a typo?'
+    )
 
 
 def test_clone_unknown_subprocess_error(mocker, clone_dir):