diff --git a/src/local/butler/scripts/oss_fuzz_backfill_issues_cc_groups.py b/src/local/butler/scripts/oss_fuzz_backfill_issues_cc_groups.py
new file mode 100644
index 00000000000..dc65860f100
--- /dev/null
+++ b/src/local/butler/scripts/oss_fuzz_backfill_issues_cc_groups.py
@@ -0,0 +1,94 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Script to backfill existing open oss-fuzz issues with the project cc group.
+
+Inspired by oss_fuzz_apply_ccs.
+"""
+
+from clusterfuzz._internal.datastore import data_handler
+from clusterfuzz._internal.datastore import data_types
+from clusterfuzz._internal.datastore import ndb_utils
+from clusterfuzz._internal.issue_management import issue_tracker_utils
+from clusterfuzz._internal.metrics import logs
+from clusterfuzz._internal.system import environment
+
+CC_GROUP_SUFFIX = '-ccs'
+
+
+def get_open_testcases_with_bugs():
+  """Return iterator to open testcases with bugs."""
+  return data_types.Testcase.query(
+      ndb_utils.is_true(data_types.Testcase.open),
+      data_types.Testcase.status == 'Processed',
+      data_types.Testcase.bug_information != '').order(  # pylint: disable=g-explicit-bool-comparison
+          data_types.Testcase.bug_information, data_types.Testcase.key)
+
+
+def get_project_cc_group(project_name: str) -> str:
+  """Return issue tracker CC group email for a project."""
+  group_domain = 'oss-fuzz.com'
+  return f'{project_name}{CC_GROUP_SUFFIX}@{group_domain}'
+
+
+def execute(args):
+  """Backfill existing open oss-fuzz issues with the cc group."""
+  del args
+  environment.set_bot_environment()
+  logs.configure('run_bot')
+  print()
+
+  testcases_failed = []
+  for testcase in get_open_testcases_with_bugs():
+    issue_tracker = issue_tracker_utils.get_issue_tracker_for_testcase(testcase)
+    if not issue_tracker:
+      logs.error(f'Failed to get issue tracker manager for {testcase.key.id()}')
+      testcases_failed.append(testcase.key.id())
+      continue
+
+    try:
+      issue = issue_tracker.get_original_issue(testcase.bug_information)
+    except Exception as e:
+      logs.error('Error occurred when fetching issue '
+                 f'{testcase.bug_information} from {testcase.key.id()}: {e}')
+      testcases_failed.append(testcase.key.id())
+      continue
+
+    if not issue or not issue.is_open:
+      continue
+
+    project_name = data_handler.get_project_name(testcase.job_type)
+    if not project_name:
+      logs.error(f'Failed to get project name from {testcase.key.id()}')
+      continue
+
+    project_cc_group = get_project_cc_group(project_name)
+    if project_cc_group in issue.ccs:
+      continue
+
+    logs.info(f'CCing {project_cc_group} on issue {issue.id}')
+    issue.ccs.add(project_cc_group)
+
+    try:
+      issue.save(notify=False)
+    except Exception as e:
+      testcases_failed.append(testcase.key.id())
+      logs.error(f'Failed to apply ccs for testcase {testcase.key.id()}: {e}')
+
+  if testcases_failed:
+    logs.error(
+        f'Failed for {len(testcases_failed)} testcases: {testcases_failed}')
+    return False
+
+  logs.info('Succeeded.')
+  return True