diff --git a/apps/api/plane/app/views/project/base.py b/apps/api/plane/app/views/project/base.py
index ec55dcb9df5..d1bd9926c83 100644
--- a/apps/api/plane/app/views/project/base.py
+++ b/apps/api/plane/app/views/project/base.py
@@ -537,6 +537,22 @@ class DeployBoardViewSet(BaseViewSet):
     serializer_class = DeployBoardSerializer
     model = DeployBoard
 
+    def get_queryset(self):
+        # SECURITY: the routed retrieve/partial_update/destroy actions are not
+        # defined on this class and fall through to DRF's ModelViewSet defaults,
+        # which resolve the object via get_object() -> get_queryset(). The base
+        # get_queryset returns DeployBoard.objects.all() (every workspace), and
+        # ProjectMemberPermission only checks the URL slug/project_id — nothing
+        # binds the object to that scope. Scope the queryset to the URL workspace
+        # + project so a foreign pk 404s instead of being read/modified/deleted
+        # cross-workspace (GHSA-h4w5-vhxc-265g).
+        return DeployBoard.objects.filter(
+            workspace__slug=self.kwargs.get("slug"),
+            entity_name="project",
+            entity_identifier=self.kwargs.get("project_id"),
+            project_id=self.kwargs.get("project_id"),
+        )
+
     def list(self, request, slug, project_id):
         project_deploy_board = DeployBoard.objects.filter(
             entity_name="project", entity_identifier=project_id, workspace__slug=slug
diff --git a/apps/api/plane/tests/contract/app/test_deploy_board_cross_workspace_scope_app.py b/apps/api/plane/tests/contract/app/test_deploy_board_cross_workspace_scope_app.py
new file mode 100644
index 00000000000..10ee6faef10
--- /dev/null
+++ b/apps/api/plane/tests/contract/app/test_deploy_board_cross_workspace_scope_app.py
@@ -0,0 +1,124 @@
+# Copyright (c) 2023-present Plane Software, Inc. and contributors
+# SPDX-License-Identifier: AGPL-3.0-only
+# See the LICENSE file for details.
+
+"""Contract tests for DeployBoardViewSet object scoping.
+
+Regression coverage for GHSA-h4w5-vhxc-265g. ``DeployBoardViewSet`` defines only
+``list``/``create``; the routed ``retrieve``/``partial_update``/``destroy`` fall
+through to DRF's ``ModelViewSet`` defaults, which resolve the object via
+``get_object()`` -> ``get_queryset()``. The base ``get_queryset`` returns
+``DeployBoard.objects.all()`` (every workspace), and ``ProjectMemberPermission``
+only checks the URL slug/project_id. So any authenticated user could supply their
+own workspace+project in the URL and a victim board's pk to read/modify/hard-delete
+another workspace's published board.
+
+The fix scopes ``get_queryset`` to the URL workspace + project, so a foreign pk
+404s.
+"""
+
+from uuid import uuid4
+
+import pytest
+from rest_framework import status
+
+from plane.db.models import DeployBoard, Project, ProjectMember, User, Workspace, WorkspaceMember
+
+
+def _board_url(slug, project_id, pk):
+    return f"/api/workspaces/{slug}/projects/{project_id}/project-deploy-boards/{pk}/"
+
+
+def _board_for(workspace, project):
+    return DeployBoard.objects.create(
+        workspace=workspace, project=project, entity_name="project", entity_identifier=project.id
+    )
+
+
+@pytest.fixture
+def project_a(db, workspace, create_user):
+    """The attacker's own project; create_user (session_client) is a member."""
+    project = Project.objects.create(
+        name="Attacker Project", identifier="ATK", workspace=workspace, created_by=create_user
+    )
+    ProjectMember.objects.create(project=project, member=create_user, workspace=workspace, role=20, is_active=True)
+    return project
+
+
+@pytest.fixture
+def own_board(db, workspace, project_a):
+    return _board_for(workspace, project_a)
+
+
+@pytest.fixture
+def sibling_board(db, workspace, create_user):
+    """A board for a DIFFERENT project in the SAME workspace as project_a.
+
+    Guards the project predicate specifically: a workspace-slug-only scope would
+    still expose this board through project_a's URL.
+    """
+    other = Project.objects.create(
+        name="Sibling Project", identifier="SIB", workspace=workspace, created_by=create_user
+    )
+    return _board_for(workspace, other)
+
+
+@pytest.fixture
+def victim_board(db):
+    """A published board in a DIFFERENT workspace the caller has no relation to."""
+    unique = uuid4().hex[:8]
+    owner = User.objects.create(email=f"victim-{unique}@plane.so", username=f"victim_{unique}")
+    owner.set_password("test-password")
+    owner.save()
+    ws = Workspace.objects.create(name="Victim WS", slug=f"victim-{unique}", owner=owner)
+    WorkspaceMember.objects.create(workspace=ws, member=owner, role=20, is_active=True)
+    project = Project.objects.create(name="Victim Project", identifier="VIC", workspace=ws, created_by=owner)
+    ProjectMember.objects.create(project=project, member=owner, workspace=ws, role=20, is_active=True)
+    return _board_for(ws, project)
+
+
+@pytest.mark.contract
+@pytest.mark.django_db
+class TestDeployBoardCrossWorkspaceScope:
+    """A caller must not reach another workspace's board via their own URL scope."""
+
+    def test_cannot_retrieve_foreign_board(self, session_client, workspace, project_a, victim_board):
+        response = session_client.get(_board_url(workspace.slug, project_a.id, victim_board.id))
+        assert response.status_code == status.HTTP_404_NOT_FOUND, (
+            f"Got {response.status_code}: {getattr(response, 'data', None)!r}"
+        )
+
+    def test_cannot_destroy_foreign_board(self, session_client, workspace, project_a, victim_board):
+        response = session_client.delete(_board_url(workspace.slug, project_a.id, victim_board.id))
+        assert response.status_code == status.HTTP_404_NOT_FOUND, (
+            f"Got {response.status_code}: {getattr(response, 'data', None)!r}"
+        )
+        assert DeployBoard.objects.filter(pk=victim_board.id).exists(), "Foreign board was deleted"
+
+    def test_cannot_patch_foreign_board(self, session_client, workspace, project_a, victim_board):
+        response = session_client.patch(
+            _board_url(workspace.slug, project_a.id, victim_board.id),
+            {"is_comments_enabled": True},
+            format="json",
+        )
+        assert response.status_code == status.HTTP_404_NOT_FOUND, (
+            f"Got {response.status_code}: {getattr(response, 'data', None)!r}"
+        )
+        victim_board.refresh_from_db()
+        assert victim_board.is_comments_enabled is False
+
+    def test_cannot_retrieve_same_workspace_other_project_board(
+        self, session_client, workspace, project_a, sibling_board
+    ):
+        """A board in the same workspace but a different project must 404 via project_a's URL."""
+        response = session_client.get(_board_url(workspace.slug, project_a.id, sibling_board.id))
+        assert response.status_code == status.HTTP_404_NOT_FOUND, (
+            f"Got {response.status_code}: {getattr(response, 'data', None)!r}"
+        )
+
+    def test_can_retrieve_own_board(self, session_client, workspace, project_a, own_board):
+        """Positive control: a project member may retrieve their own board."""
+        response = session_client.get(_board_url(workspace.slug, project_a.id, own_board.id))
+        assert response.status_code == status.HTTP_200_OK, (
+            f"Got {response.status_code}: {getattr(response, 'data', None)!r}"
+        )