diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 9c9d083b..112353f6 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -1,3 +1,7 @@
+## 2026-08-15 - [Sentinel: Uncontrolled Resource Consumption in Job Cleanup]
+**Vulnerability:** Resource Exhaustion (CWE-400 / CWE-770) via unretrieved job results.
+**Learning:** When successful jobs only clean up their temporary directories upon result download, an attacker can intentionally create jobs and abandon them to exhaust disk space or inodes over time.
+**Prevention:** Implement an automatic cleanup mechanism (like a background sweep or TTL) for jobs that complete but are never retrieved.
 ## 2026-07-25 - [Cross-platform upload basename normalization]
 **Behavior:** Upload metadata now interprets both forward slashes and backslashes as path separators before extracting a basename.
 **Learning:** On POSIX systems, `pathlib.Path(filename).name` retains backslashes because they are ordinary characters there. That caused inconsistent manifest and converter filenames for Windows-style client paths. The upload itself is still written inside a trusted temporary workspace, and batch archive entry names are generated outputs; this change does not establish a filesystem traversal or archive-entry escape.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9313538b..a1d2f1eb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,3 +12,6 @@
 ### Fixed
 - 단일·일괄 대상 크기 입력을 비웠을 때 이전 custom validity와 `aria-invalid` 상태를 즉시 초기화해 현재 필수 입력 상태를 정확히 전달합니다.
 - 업로드 파일명의 경로 구분자를 정규화하여 POSIX에서도 Windows 형식의 클라이언트 경로가 일관된 basename으로 기록되도록 수정했습니다.
+
+### 보안
+- 완료된 비동기 작업의 결과가 다운로드되지 않을 때 임시 디렉터리가 무한정 쌓이는 리소스 고갈(DoS) 취약점을 방지하기 위해 24시간 후 만료된 작업을 자동 정리하도록 수정했습니다.
diff --git a/saas_web.py b/saas_web.py
index 63265e94..1c6a2de4 100644
--- a/saas_web.py
+++ b/saas_web.py
@@ -797,6 +797,20 @@ def _run_job(
         cleanup_temp_dir(temp_dir_path)
 
 
+def _cleanup_expired_jobs() -> None:
+    """Remove jobs and their temporary workspaces that have been finished for over 24 hours."""
+    from datetime import timedelta
+    store = _get_job_store()
+    now = _now()
+    for job in store.list_jobs():
+        if job["status"] in ("done", "failed"):
+            try:
+                updated_at = datetime.fromisoformat(job["updated_at"])
+                if now - updated_at > timedelta(hours=24):
+                    _cleanup_job(job["id"])
+            except Exception:
+                logger.exception("Failed to parse updated_at for job %s", job["id"])
+
 @app.post("/jobs")
 def submit_job(
     background_tasks: BackgroundTasks,
@@ -804,6 +818,7 @@ def submit_job(
     target_bytes: int = Form(2_000_000_000),
 ):
     """Enqueue a shrink job and return its id for asynchronous status polling."""
+    background_tasks.add_task(_cleanup_expired_jobs)
     error = _validate_request(file, target_bytes)
     if error is not None:
         return JSONResponse(status_code=400, content={"error": error})
diff --git a/tests/test_saas_web.py b/tests/test_saas_web.py
index 3b57e033..e2409337 100644
--- a/tests/test_saas_web.py
+++ b/tests/test_saas_web.py
@@ -1173,6 +1173,31 @@ def test_cleanup_job_removes_workspace(self):
         self.assertFalse(temp_dir.exists())
         self.assertIsNone(saas_web.JOB_STORE.get("c"))
 
+    @patch("saas_web._cleanup_job")
+    @patch("saas_web._get_job_store")
+    def test_cleanup_expired_jobs(self, mock_get_store, mock_cleanup):
+        from datetime import datetime, timezone, timedelta
+        mock_store = MagicMock()
+        mock_get_store.return_value = mock_store
+
+        now = datetime.now(timezone.utc)
+        past_time_1 = (now - timedelta(hours=25)).isoformat()
+        past_time_2 = (now - timedelta(hours=10)).isoformat()
+
+        mock_store.list_jobs.return_value = [
+            {"id": "job_1", "status": "done", "updated_at": past_time_1},
+            {"id": "job_2", "status": "done", "updated_at": past_time_2},
+            {"id": "job_3", "status": "processing", "updated_at": past_time_1},
+            {"id": "job_4", "status": "failed", "updated_at": past_time_1},
+            {"id": "job_5", "status": "failed", "updated_at": "invalid-time"},
+        ]
+
+        saas_web._cleanup_expired_jobs()
+
+        mock_cleanup.assert_any_call("job_1")
+        mock_cleanup.assert_any_call("job_4")
+        self.assertEqual(mock_cleanup.call_count, 2)
+
     def test_cleanup_job_tolerates_unknown_job(self):
         saas_web._cleanup_job("unknown-cleanup-job")
         self.assertIsNone(saas_web.JOB_STORE.get("unknown-cleanup-job"))