diff --git a/apps/api/plane/api/views/project.py b/apps/api/plane/api/views/project.py
index 77a195bdec..30f61f08d3 100644
--- a/apps/api/plane/api/views/project.py
+++ b/apps/api/plane/api/views/project.py
@@ -49,7 +49,11 @@ from plane.api.serializers import (
     ProjectCreateSerializer,
     ProjectUpdateSerializer,
 )
-from plane.app.permissions import ProjectBasePermission, WorkSpaceAdminPermission
+from plane.app.permissions import (
+    ProjectArchiveUnarchivePermission,
+    ProjectBasePermission,
+    WorkSpaceAdminPermission,
+)
 from plane.utils.openapi import (
     project_docs,
     PROJECT_ID_PARAMETER,
@@ -649,7 +653,10 @@ class ProjectDetailAPIEndpoint(BaseAPIView):
 class ProjectArchiveUnarchiveAPIEndpoint(BaseAPIView):
     """Project Archive and Unarchive Endpoint"""
 
-    permission_classes = [ProjectBasePermission]
+    # Not ProjectBasePermission: its POST branch is written for project
+    # creation (workspace-role check only, no project_id binding) and archive
+    # is not creation — see ProjectArchiveUnarchivePermission's docstring.
+    permission_classes = [ProjectArchiveUnarchivePermission]
 
     @project_docs(
         operation_id="archive_project",
diff --git a/apps/api/plane/app/permissions/__init__.py b/apps/api/plane/app/permissions/__init__.py
index 457a13cb7b..a0bef7d89a 100644
--- a/apps/api/plane/app/permissions/__init__.py
+++ b/apps/api/plane/app/permissions/__init__.py
@@ -13,6 +13,7 @@ from .workspace import (
 )
 from .project import (
     ProjectBasePermission,
+    ProjectArchiveUnarchivePermission,
     ProjectEntityPermission,
     ProjectMemberPermission,
     ProjectLitePermission,
diff --git a/apps/api/plane/app/permissions/project.py b/apps/api/plane/app/permissions/project.py
index 5a07bdefe5..81c3724fa1 100644
--- a/apps/api/plane/app/permissions/project.py
+++ b/apps/api/plane/app/permissions/project.py
@@ -53,6 +53,50 @@ class ProjectBasePermission(BasePermission):
             )
 
 
+class ProjectArchiveUnarchivePermission(BasePermission):
+    """Archive/unarchive always target an existing project_id — never project
+    creation — so this must not share ProjectBasePermission's POST branch,
+    which assumes POST means "create a project" and checks only
+    workspace-level role with no project_id binding at all. A workspace
+    ADMIN/MEMBER with no ProjectMember row on the target project could
+    otherwise archive (and delete every UserFavorite row on) a project they
+    cannot even read.
+
+    Mirrors the app-layer twin's gate (``allow_permission([ROLE.ADMIN,
+    ROLE.MEMBER])``, ``level="PROJECT"`` default) on both post and delete so
+    the two verbs agree — unarchive already got this right by falling
+    through to ProjectBasePermission's non-POST branch; archive didn't.
+    """
+
+    def has_permission(self, request, view):
+        if request.user.is_anonymous:
+            return False
+
+        if ProjectMember.objects.filter(
+            workspace__slug=view.workspace_slug,
+            member=request.user,
+            project_id=view.project_id,
+            role__in=[ROLE.ADMIN.value, ROLE.MEMBER.value],
+            is_active=True,
+        ).exists():
+            return True
+
+        return (
+            ProjectMember.objects.filter(
+                workspace__slug=view.workspace_slug,
+                member=request.user,
+                project_id=view.project_id,
+                is_active=True,
+            ).exists()
+            and WorkspaceMember.objects.filter(
+                member=request.user,
+                workspace__slug=view.workspace_slug,
+                role=ROLE.ADMIN.value,
+                is_active=True,
+            ).exists()
+        )
+
+
 class ProjectMemberPermission(BasePermission):
     def has_permission(self, request, view):
         if request.user.is_anonymous:
diff --git a/apps/api/plane/tests/contract/api/test_project_archive_scope.py b/apps/api/plane/tests/contract/api/test_project_archive_scope.py
new file mode 100644
index 0000000000..cc17630e5f
--- /dev/null
+++ b/apps/api/plane/tests/contract/api/test_project_archive_scope.py
@@ -0,0 +1,125 @@
+# Copyright (c) 2023-present Plane Software, Inc. and contributors
+# SPDX-License-Identifier: AGPL-3.0-only
+# See the LICENSE file for details.
+
+"""Regression test for project-archive authorization bypass on the external API.
+
+Root cause: ProjectArchiveUnarchiveAPIEndpoint used ProjectBasePermission,
+whose POST branch is written for project creation — it checks only
+workspace-level role (ADMIN/MEMBER) with no project_id binding at all. Since
+archive is POST but is not creation, any active workspace member could
+archive (and delete every UserFavorite row on) any project in the workspace,
+including a fully private one they have no ProjectMember row on and cannot
+otherwise read.
+
+DELETE (unarchive) was never affected — it falls through to
+ProjectBasePermission's non-POST branch, which does check project membership.
+So this was specifically an asymmetry between the two verbs of the same
+endpoint.
+
+Fixed by giving the endpoint its own ProjectArchiveUnarchivePermission,
+scoped to project_id, mirroring the app-layer twin's gate (active
+ProjectMember with role ADMIN or MEMBER, or any active ProjectMember plus a
+workspace ADMIN role) — applied to both post and delete.
+"""
+
+from uuid import uuid4
+
+import pytest
+from rest_framework import status
+from rest_framework.test import APIClient
+
+from plane.db.models import APIToken, Project, ProjectMember, User, WorkspaceMember
+
+pytestmark = pytest.mark.contract
+
+
+def _make_user(prefix):
+    unique = uuid4().hex[:8]
+    user = User.objects.create(email=f"{prefix}-{unique}@plane.so", username=f"{prefix}_{unique}")
+    user.set_password("test-password")
+    user.save()
+    return user
+
+
+def _client_for(user):
+    token = APIToken.objects.create(user=user, label="Test Token", token=f"token-{uuid4().hex}")
+    client = APIClient()
+    client.credentials(HTTP_X_API_KEY=token.token)
+    return client
+
+
+@pytest.fixture
+def private_project(db, workspace, create_user):
+    """A fully private (network=0) project owned by create_user, the
+    workspace admin (via the `workspace` fixture)."""
+    project = Project.objects.create(
+        name="Confidential",
+        identifier="CONF",
+        workspace=workspace,
+        created_by=create_user,
+        network=0,
+    )
+    ProjectMember.objects.create(project=project, workspace=workspace, member=create_user, role=20, is_active=True)
+    return project
+
+
+@pytest.fixture
+def attacker_member(db, workspace):
+    """An active workspace MEMBER (role 15) with no ProjectMember row on
+    private_project — the attacker in this advisory."""
+    user = _make_user("attacker")
+    WorkspaceMember.objects.create(workspace=workspace, member=user, role=15, is_active=True)
+    return user
+
+
+def _archive_url(slug, project_id):
+    return f"/api/v1/workspaces/{slug}/projects/{project_id}/archive/"
+
+
+@pytest.mark.django_db
+class TestProjectArchiveScope:
+    def test_workspace_member_without_project_membership_cannot_archive(
+        self, workspace, private_project, attacker_member
+    ):
+        client = _client_for(attacker_member)
+
+        response = client.post(_archive_url(workspace.slug, private_project.id))
+
+        assert response.status_code == status.HTTP_403_FORBIDDEN, f"got {response.status_code}: {response.data!r}"
+        private_project.refresh_from_db()
+        assert private_project.archived_at is None, "the project must not have been archived"
+
+    def test_workspace_member_without_project_membership_cannot_unarchive(
+        self, workspace, private_project, attacker_member
+    ):
+        """Symmetry check: unarchive was already correctly gated before this
+        fix — must still be, now that archive shares the same permission
+        class."""
+        client = _client_for(attacker_member)
+
+        response = client.delete(_archive_url(workspace.slug, private_project.id))
+
+        assert response.status_code == status.HTTP_403_FORBIDDEN, f"got {response.status_code}: {response.data!r}"
+
+    def test_project_member_can_archive_and_unarchive_their_own_project(self, workspace, private_project):
+        """Positive control: an active project MEMBER (not just admin) must
+        still be able to archive/unarchive — the fix must not overtighten
+        beyond the app-layer twin's ADMIN-or-MEMBER gate."""
+        member_user = _make_user("member")
+        WorkspaceMember.objects.create(workspace=workspace, member=member_user, role=15, is_active=True)
+        ProjectMember.objects.create(
+            project=private_project, workspace=workspace, member=member_user, role=15, is_active=True
+        )
+        client = _client_for(member_user)
+        url = _archive_url(workspace.slug, private_project.id)
+
+        response = client.post(url)
+        assert response.status_code == status.HTTP_204_NO_CONTENT, f"got {response.status_code}: {response.data!r}"
+        private_project.refresh_from_db()
+        assert private_project.archived_at is not None
+
+        response = client.delete(url)
+        assert response.status_code == status.HTTP_204_NO_CONTENT, f"got {response.status_code}: {response.data!r}"
+        private_project.refresh_from_db()
+        assert private_project.archived_at is None