diff --git a/kernelguard.py b/kernelguard.py
index f086847..4e29bc2 100644
--- a/kernelguard.py
+++ b/kernelguard.py
@@ -2462,6 +2462,163 @@ def _has_ver(expr: ast.AST | None) -> bool:
     return []
 
 
+def detect_setattr_box_replay(code: str | SubmissionFacts) -> list[dict]:
+    """Pattern: replay state stored on an object through setattr."""
+    facts = ensure_submission_facts(code)
+    tree = facts.ast_tree
+    if tree is None:
+        return []
+    entrypoint_name = entrypoint_label(facts.entrypoint_name)
+
+    strings = {
+        target.id: stmt.value.value
+        for stmt in tree.body
+        if isinstance(stmt, ast.Assign)
+        and len(stmt.targets) == 1
+        and isinstance(stmt.targets[0], ast.Name)
+        and isinstance(stmt.value, ast.Constant)
+        and isinstance(stmt.value.value, str)
+        for target in stmt.targets
+    }
+
+    objects = {
+        stmt.targets[0].id
+        for stmt in tree.body
+        if isinstance(stmt, ast.Assign)
+        and len(stmt.targets) == 1
+        and isinstance(stmt.targets[0], ast.Name)
+        and isinstance(stmt.value, ast.Call)
+    }
+
+    def _string_value(expr: ast.AST | None) -> str | None:
+        if isinstance(expr, ast.Constant) and isinstance(expr.value, str):
+            return expr.value
+        if isinstance(expr, ast.Name):
+            return strings.get(expr.id)
+        return None
+
+    def _object_attr(expr: ast.AST | None) -> tuple[str, str] | None:
+        if (
+            isinstance(expr, ast.Attribute)
+            and isinstance(expr.value, ast.Name)
+            and expr.value.id in objects
+        ):
+            return expr.value.id, expr.attr
+        if (
+            isinstance(expr, ast.Call)
+            and isinstance(expr.func, ast.Name)
+            and expr.func.id == "getattr"
+            and len(expr.args) >= 2
+            and isinstance(expr.args[0], ast.Name)
+            and expr.args[0].id in objects
+        ):
+            attr = _string_value(expr.args[1])
+            if attr:
+                return expr.args[0].id, attr
+        return None
+
+    def _hasattr_key(expr: ast.AST) -> tuple[str, str] | None:
+        if not (
+            isinstance(expr, ast.Call)
+            and isinstance(expr.func, ast.Name)
+            and expr.func.id == "hasattr"
+            and len(expr.args) >= 2
+            and isinstance(expr.args[0], ast.Name)
+            and expr.args[0].id in objects
+        ):
+            return None
+        attr = _string_value(expr.args[1])
+        if attr:
+            return expr.args[0].id, attr
+        return None
+
+    def _setattr_key(expr: ast.AST, params: set[str]) -> tuple[str, str] | None:
+        if not isinstance(expr, ast.Call):
+            return None
+
+        args = expr.args
+        direct_setattr = isinstance(expr.func, ast.Name) and expr.func.id == "setattr"
+        object_setattr = (
+            isinstance(expr.func, ast.Attribute)
+            and expr.func.attr == "__setattr__"
+            and isinstance(expr.func.value, ast.Name)
+            and expr.func.value.id == "object"
+        )
+        if not (direct_setattr or object_setattr):
+            return None
+        if len(args) < 3 or not isinstance(args[0], ast.Name) or args[0].id not in objects:
+            return None
+        if not (_expr_names(args[2]) & params):
+            return None
+        if not any(isinstance(node, ast.Call) for node in ast.walk(args[2])):
+            return None
+
+        attr = _string_value(args[1])
+        if attr:
+            return args[0].id, attr
+        return None
+
+    def _body_has_real_calls(body: list[ast.stmt]) -> bool:
+        for stmt in body:
+            for expr in ast.walk(stmt):
+                if not isinstance(expr, ast.Call):
+                    continue
+                if _object_attr(expr) is not None:
+                    continue
+                return True
+        return False
+
+    for node in ast.walk(tree):
+        if not isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef)):
+            continue
+        if not is_entrypoint_name(node.name):
+            continue
+
+        params = {arg.arg for arg in node.args.args}
+        params.update(arg.arg for arg in node.args.posonlyargs)
+        params.update(arg.arg for arg in node.args.kwonlyargs)
+
+        mutated = {
+            key
+            for child in ast.walk(node)
+            for key in [_setattr_key(child, params)]
+            if key is not None
+        }
+        if not mutated:
+            continue
+
+        for child in ast.walk(node):
+            if not isinstance(child, ast.If):
+                continue
+            if _body_has_real_calls(child.body):
+                continue
+
+            tested = {
+                key
+                for expr in ast.walk(child.test)
+                for key in (_hasattr_key(expr), _object_attr(expr))
+                if key is not None
+            }
+            returned = {
+                key
+                for stmt in child.body
+                if isinstance(stmt, ast.Return)
+                for key in [_object_attr(stmt.value)]
+                if key is not None
+            }
+            if tested & returned & mutated:
+                return [{
+                    "pattern": "SETATTR_BOX_REPLAY",
+                    "severity": "critical",
+                    "evidence": (
+                        f"{entrypoint_name} returns object attribute state "
+                        "populated from a prior input through setattr"
+                    ),
+                }]
+
+    return []
+
+
 RE_OBJECT_ID_DATA = re.compile(r"\bdata_id\s*=\s*id\s*\(\s*data\s*\)")
 RE_RESULT_BANK_SET = re.compile(r"_superbatch_results\s*\[\s*(?:did|data_id)\s*\]\s*=")
 RE_RESULT_BANK_RETURN = re.compile(r"return\s+_superbatch_results\s*\[\s*data_id\s*\]")
@@ -3479,6 +3636,10 @@ class RulePolicy:
         "LAST_CALL_REPLAY", "result_reuse", "hard", AUTO_FILTER, (),
         AMD_MANUAL_LAST_CALL_REPLAY_FIXTURES, "keep",
     ),
+    "SETATTR_BOX_REPLAY": RulePolicy(
+        "SETATTR_BOX_REPLAY", "result_reuse", "hard", AUTO_FILTER, (),
+        (), "keep",
+    ),
     "SHAPE_OUTPUT_REPLAY": RulePolicy(
         "SHAPE_OUTPUT_REPLAY", "result_reuse", "hard", AUTO_FILTER, (),
         AMD_PACKAGE_SHAPE_REPLAY_FIXTURES, "keep",
@@ -3762,6 +3923,7 @@ def support_only_patterns(matched_patterns: list[dict]) -> bool:
     detect_decode_mm_ref,
     detect_result_caching,
     detect_last_call_replay,
+    detect_setattr_box_replay,
     detect_shape_output_replay,
     detect_timed_input_replay,
     detect_cuda_graph_replay,
@@ -3800,6 +3962,7 @@ def support_only_patterns(matched_patterns: list[dict]) -> bool:
     ("decode_mm_ref", detect_decode_mm_ref),
     ("result_caching", detect_result_caching),
     ("last_call_replay", detect_last_call_replay),
+    ("setattr_box_replay", detect_setattr_box_replay),
     ("shape_output_replay", detect_shape_output_replay),
     ("timed_input_replay", detect_timed_input_replay),
     ("cuda_graph_replay", detect_cuda_graph_replay),
@@ -4696,7 +4859,7 @@ def _worker_parquet(args: tuple) -> dict:
     "EVALUATOR_EXPLOIT", "HARNESS_RUNTIME_PATCHING", "MODULE_MUTATION", "GLOBALS_MUTATION", "CODE_REPLACEMENT",
     "FRAME_WALK_ACCESS", "FRAME_WALK_MUTATION", "SYS_MODULES_ACCESS", "GLOBALS_ACCESS", "CODE_ACCESS",
     "TRUSTED_MODULE_IMPORT",
-    "OUTPUT_REPLAY_CACHE", "LAST_CALL_REPLAY", "SHAPE_OUTPUT_REPLAY", "TIMED_INPUT_REPLAY", "CONFIG_CACHE_EXPLOIT", "POINTER_REPLAY", "RESULT_BANK_REPLAY", "PREPROCESS_CACHE", "WORKSPACE_CACHE",
+    "OUTPUT_REPLAY_CACHE", "LAST_CALL_REPLAY", "SETATTR_BOX_REPLAY", "SHAPE_OUTPUT_REPLAY", "TIMED_INPUT_REPLAY", "CONFIG_CACHE_EXPLOIT", "POINTER_REPLAY", "RESULT_BANK_REPLAY", "PREPROCESS_CACHE", "WORKSPACE_CACHE",
     "RUNNER_PLAN_CACHE", "CUDA_GRAPH_PYTHON", "CUDA_GRAPH_REPLAY",
     "TIMER_MONKEYPATCH", "FAKE_BENCHMARK_EMIT", "STDIO_REDIRECT", "UNSYNC_MULTISTREAM", "CUDA_EVENT_DISABLE_TIMING",
     "SCALED_MM_REF", "DECODE_MM_REF", "SILENT_FALLBACK", "REFERENCE_PRECOMPUTE_REPLAY", "TORCH_COMPILE_CACHE",