diff --git a/apps/api/plane/app/serializers/project.py b/apps/api/plane/app/serializers/project.py
index aef296bc6c2..13e6e7e2e40 100644
--- a/apps/api/plane/app/serializers/project.py
+++ b/apps/api/plane/app/serializers/project.py
@@ -34,7 +34,12 @@ class ProjectSerializer(BaseSerializer):
     class Meta:
         model = Project
         fields = "__all__"
-        read_only_fields = ["workspace", "deleted_at"]
+        # created_by/updated_by are audit fields set server-side by BaseModel.save()
+        # from the request user; with fields="__all__" they are otherwise client-writable,
+        # letting a caller forge project ownership/attribution. save() only backfills
+        # created_by when it is None, so a supplied value would survive — mark them
+        # read-only so the client value is ignored.
+        read_only_fields = ["workspace", "deleted_at", "created_by", "updated_by"]
 
     def validate_name(self, name):
         project_id = self.instance.id if self.instance else None
diff --git a/apps/api/plane/tests/unit/utils/test_paginator.py b/apps/api/plane/tests/unit/utils/test_paginator.py
index b249f4d184b..2e2b6a60ec8 100644
--- a/apps/api/plane/tests/unit/utils/test_paginator.py
+++ b/apps/api/plane/tests/unit/utils/test_paginator.py
@@ -121,3 +121,55 @@ def test_no_group_by_is_unaffected(self):
             paginator_cls=_StubGroupedPaginator,
         )
         assert response.data["grouped_by"] is None
+
+
+class _ExplodingPaginator:
+    """Fails if constructed — proves the cursor guard rejects BEFORE any paginator runs."""
+
+    def __init__(self, **kwargs):
+        raise AssertionError("paginator_cls must not be constructed for an invalid cursor")
+
+
+@pytest.mark.unit
+class TestCursorBounds:
+    """paginate() must reject an out-of-bounds client cursor before it drives slicing.
+
+    The grouped paginators use cursor.value as the per-group page size
+    (stop = offset + (cursor.value or limit) + 1). A negative value slices the queryset
+    with a negative stop -> ValueError('Negative indexing is not supported') -> HTTP 500;
+    a huge value fetches far more than max_per_page rows per group (cap bypass / DoS).
+    cursor.offset must be non-negative."""
+
+    @pytest.mark.parametrize("cursor", ["-1:0:0", "1000000:0:0", "20:-1:0"])
+    def test_out_of_bounds_cursor_rejected_before_paginator(self, cursor):
+        request = _make_request(cursor=cursor)
+        with pytest.raises(ParseError):
+            BasePaginator().paginate(
+                request=request,
+                queryset=None,
+                paginator_cls=_ExplodingPaginator,
+                default_per_page=20,
+                max_per_page=1000,
+            )
+
+    def test_valid_cursor_passes_the_guard(self):
+        request = _make_request(cursor="20:0:0")
+        response = BasePaginator().paginate(
+            request=request,
+            queryset=None,
+            paginator_cls=_StubGroupedPaginator,
+            default_per_page=20,
+            max_per_page=1000,
+        )
+        assert response.data["results"] == []
+
+    def test_cursor_value_at_max_is_allowed(self):
+        request = _make_request(cursor="1000:0:0")
+        response = BasePaginator().paginate(
+            request=request,
+            queryset=None,
+            paginator_cls=_StubGroupedPaginator,
+            default_per_page=20,
+            max_per_page=1000,
+        )
+        assert response.data["results"] == []
diff --git a/apps/api/plane/utils/paginator.py b/apps/api/plane/utils/paginator.py
index 2082041f1ac..3ff29213834 100644
--- a/apps/api/plane/utils/paginator.py
+++ b/apps/api/plane/utils/paginator.py
@@ -680,6 +680,17 @@ def paginate(
         except ValueError:
             raise ParseError(detail="Invalid cursor parameter.")
 
+        # Bound the client-supplied cursor before it drives any slicing. The grouped
+        # paginators use cursor.value as the per-group page size
+        # (stop = offset + (cursor.value or limit) + 1). Left unbounded, a negative value
+        # slices the queryset with a negative stop -> "Negative indexing is not supported"
+        # (HTTP 500), and a huge value fetches far more than max_per_page rows per group
+        # (max_per_page cap bypass / resource-exhaustion DoS). cursor.offset is the page
+        # index and must be non-negative.
+        effective_max_per_page = max(max_per_page, default_per_page)
+        if not (0 <= input_cursor.value <= effective_max_per_page) or input_cursor.offset < 0:
+            raise ParseError(detail="Invalid cursor parameter.")
+
         if not paginator:
             if group_by_field_name:
                 # Validate against the allowlist before the field name reaches