diff --git a/backend/app/core/security.py b/backend/app/core/security.py
index ee9257a..957b1aa 100644
--- a/backend/app/core/security.py
+++ b/backend/app/core/security.py
@@ -1,22 +1,22 @@
 from datetime import datetime, timedelta, timezone
 
+import bcrypt
 from jose import JWTError, jwt
-from passlib.context import CryptContext
 
 from app.core.config import settings
 
-pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
-
 
 def verify_password(plain: str, hashed: str) -> bool:
+    if not plain or not hashed:
+        return False
     try:
-        return bool(pwd_context.verify(plain, hashed))
-    except ValueError:
+        return bcrypt.checkpw(plain.encode("utf-8"), hashed.encode("utf-8"))
+    except (ValueError, TypeError):
         return False
 
 
 def hash_password(password: str) -> str:
-    return str(pwd_context.hash(password))
+    return bcrypt.hashpw(password.encode("utf-8"), bcrypt.gensalt()).decode("utf-8")
 
 
 def create_access_token(subject: str) -> str:
diff --git a/backend/app/services/status_checker.py b/backend/app/services/status_checker.py
index 4f6ba75..8a75126 100644
--- a/backend/app/services/status_checker.py
+++ b/backend/app/services/status_checker.py
@@ -24,6 +24,11 @@ async def check_node(check_method: str, target: str | None, ip: str | None) -> d
     host = target or raw_ip
     if not host:
         return {"status": "unknown", "response_time_ms": None}
+    # Reject hostnames that look like CLI flags — defends ping/tcp invocations
+    # against arg-injection if a malicious admin sets target like "-O".
+    if host.startswith("-"):
+        logger.warning("Rejecting check target that starts with '-': %r", host)
+        return {"status": "unknown", "response_time_ms": None}
 
     start = time.monotonic()
     try:
diff --git a/backend/requirements.txt b/backend/requirements.txt
index e504051..53d5bb7 100644
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@@ -7,8 +7,7 @@ alembic==1.13.3
 pydantic==2.9.2
 pydantic-settings==2.5.2
 python-jose[cryptography]==3.5.0
-passlib[bcrypt]==1.7.4
-bcrypt==4.0.1
+bcrypt==4.2.1
 python-multipart==0.0.27
 apscheduler==3.10.4
 python-nmap==0.7.1
diff --git a/backend/scripts/hash_password.py b/backend/scripts/hash_password.py
index 9ee5c5b..6c1587d 100644
--- a/backend/scripts/hash_password.py
+++ b/backend/scripts/hash_password.py
@@ -1,13 +1,11 @@
-"""Generate a bcrypt password hash for config.yml."""
+"""Generate a bcrypt password hash for the AUTH_PASSWORD_HASH env var."""
 import sys
 
-from passlib.context import CryptContext
-
-pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+import bcrypt
 
 if len(sys.argv) < 2:
     print("Usage: python scripts/hash_password.py <password>")
     sys.exit(1)
 
 password = sys.argv[1]
-print(pwd_context.hash(password))
+print(bcrypt.hashpw(password.encode("utf-8"), bcrypt.gensalt()).decode("utf-8"))
diff --git a/backend/tests/conftest.py b/backend/tests/conftest.py
index de3d6dd..7dc8c21 100644
--- a/backend/tests/conftest.py
+++ b/backend/tests/conftest.py
@@ -5,23 +5,21 @@ os.environ.setdefault("SECRET_KEY", "test-only-secret-key-not-for-production")
 
 import pytest
 from httpx import ASGITransport, AsyncClient
-from passlib.context import CryptContext
 from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 
+from app.core.security import hash_password
 from app.db.database import Base, get_db
 from app.main import app
 
 TEST_DB_URL = "sqlite+aiosqlite:///:memory:"
 
-_pwd_ctx = CryptContext(schemes=["bcrypt"], deprecated="auto")
-
 
 @pytest.fixture(autouse=True, scope="session")
 def test_credentials():
     """Configure test auth credentials directly on settings."""
     from app.core.config import settings
     settings.auth_username = "admin"
-    settings.auth_password_hash = _pwd_ctx.hash("admin")
+    settings.auth_password_hash = hash_password("admin")
 
 
 @pytest.fixture
diff --git a/backend/tests/test_auth.py b/backend/tests/test_auth.py
index f65f578..09b569d 100644
--- a/backend/tests/test_auth.py
+++ b/backend/tests/test_auth.py
@@ -68,3 +68,71 @@ async def test_login_with_malformed_hash_returns_401_not_500(client: AsyncClient
         assert res.status_code == 401
     finally:
         settings.auth_password_hash = original
+
+
+# --- JWT-level cases ---
+
+async def test_expired_token_rejected(client: AsyncClient):
+    """A JWT whose `exp` is in the past must be refused."""
+    from datetime import datetime, timedelta, timezone
+
+    from jose import jwt
+
+    from app.core.config import settings
+    payload = {
+        "sub": "admin",
+        "exp": datetime.now(timezone.utc) - timedelta(minutes=1),
+    }
+    token = jwt.encode(payload, settings.secret_key, algorithm=settings.algorithm)
+    res = await client.get("/api/v1/nodes", headers={"Authorization": f"Bearer {token}"})
+    assert res.status_code == 401
+
+
+async def test_malformed_token_rejected(client: AsyncClient):
+    res = await client.get("/api/v1/nodes", headers={"Authorization": "Bearer not-a-jwt"})
+    assert res.status_code == 401
+
+
+async def test_token_signed_with_wrong_secret_rejected(client: AsyncClient):
+    """A token signed with a different key must not be accepted."""
+    from datetime import datetime, timedelta, timezone
+
+    from jose import jwt
+
+    from app.core.config import settings
+    payload = {
+        "sub": "admin",
+        "exp": datetime.now(timezone.utc) + timedelta(minutes=5),
+    }
+    forged = jwt.encode(payload, "different-secret", algorithm=settings.algorithm)
+    res = await client.get("/api/v1/nodes", headers={"Authorization": f"Bearer {forged}"})
+    assert res.status_code == 401
+
+
+async def test_missing_authorization_header_rejected(client: AsyncClient):
+    res = await client.get("/api/v1/nodes")
+    assert res.status_code == 401
+
+
+async def test_empty_password_does_not_pass_when_hash_empty(client: AsyncClient):
+    """No credentials configured server-side must not authenticate an empty password."""
+    from app.core.config import settings
+    original_hash = settings.auth_password_hash
+    settings.auth_password_hash = ""
+    try:
+        res = await client.post("/api/v1/auth/login", json={"username": "admin", "password": ""})
+        assert res.status_code == 401
+    finally:
+        settings.auth_password_hash = original_hash
+
+
+# --- Password helper ---
+
+def test_verify_password_handles_empty_inputs():
+    """verify_password must be safe against empty plain / empty hash without raising."""
+    from app.core.security import hash_password, verify_password
+    h = hash_password("hunter2")
+    assert verify_password("hunter2", h) is True
+    assert verify_password("", h) is False
+    assert verify_password("hunter2", "") is False
+    assert verify_password("", "") is False
diff --git a/backend/tests/test_scan.py b/backend/tests/test_scan.py
index 6b4b640..7199ea9 100644
--- a/backend/tests/test_scan.py
+++ b/backend/tests/test_scan.py
@@ -37,6 +37,95 @@ async def pending_device(db_session):
     return device
 
 
+# --- _background_scan error handling ---
+
+@pytest.fixture
+async def mem_db():
+    from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+
+    from app.db.database import Base
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    factory = async_sessionmaker(engine, expire_on_commit=False)
+    yield factory
+    await engine.dispose()
+
+
+@pytest.mark.asyncio
+async def test_background_scan_marks_run_failed_on_exception(mem_db):
+    """If run_scan() raises, the ScanRun must transition running → failed and the
+    session rollback path must execute without a follow-on exception."""
+    from app.api.routes.scan import _background_scan
+
+    async with mem_db() as session:
+        run = ScanRun(status="running", ranges=["10.0.0.0/24"])
+        session.add(run)
+        await session.commit()
+        run_id = run.id
+
+    with (
+        patch("app.api.routes.scan.AsyncSessionLocal", mem_db),
+        patch(
+            "app.api.routes.scan.run_scan",
+            new_callable=AsyncMock,
+            side_effect=RuntimeError("boom"),
+        ),
+    ):
+        await _background_scan(run_id, ["10.0.0.0/24"])
+
+    async with mem_db() as session:
+        refreshed = await session.get(ScanRun, run_id)
+        assert refreshed is not None
+        assert refreshed.status == "failed"
+
+
+@pytest.mark.asyncio
+async def test_background_scan_leaves_non_running_status_alone(mem_db):
+    """If the run was already stopped/cancelled before run_scan failed, _background_scan
+    must NOT overwrite that terminal status with 'failed'."""
+    from app.api.routes.scan import _background_scan
+
+    async with mem_db() as session:
+        run = ScanRun(status="cancelled", ranges=["10.0.0.0/24"])
+        session.add(run)
+        await session.commit()
+        run_id = run.id
+
+    with (
+        patch("app.api.routes.scan.AsyncSessionLocal", mem_db),
+        patch(
+            "app.api.routes.scan.run_scan",
+            new_callable=AsyncMock,
+            side_effect=RuntimeError("boom"),
+        ),
+    ):
+        await _background_scan(run_id, ["10.0.0.0/24"])
+
+    async with mem_db() as session:
+        refreshed = await session.get(ScanRun, run_id)
+        assert refreshed is not None
+        assert refreshed.status == "cancelled"
+
+
+@pytest.mark.asyncio
+async def test_background_scan_success_path_invokes_run_scan(mem_db):
+    from app.api.routes.scan import _background_scan
+
+    async with mem_db() as session:
+        run = ScanRun(status="running", ranges=["10.0.0.0/24"])
+        session.add(run)
+        await session.commit()
+        run_id = run.id
+
+    with (
+        patch("app.api.routes.scan.AsyncSessionLocal", mem_db),
+        patch("app.api.routes.scan.run_scan", new_callable=AsyncMock) as mock_run_scan,
+    ):
+        await _background_scan(run_id, ["10.0.0.0/24"])
+        mock_run_scan.assert_awaited_once()
+
+
 # --- Trigger scan ---
 
 @pytest.mark.asyncio
diff --git a/backend/tests/test_status_checker.py b/backend/tests/test_status_checker.py
index 3d23cd8..205e62d 100644
--- a/backend/tests/test_status_checker.py
+++ b/backend/tests/test_status_checker.py
@@ -216,6 +216,31 @@ async def test_ping_uses_windows_args_on_win32():
     assert "-c" not in captured["args"]
 
 
+# --- check_node target validation ---
+
+@pytest.mark.asyncio
+async def test_check_node_rejects_flag_like_target():
+    """A target starting with '-' must never reach subprocess invocation."""
+    from app.services.status_checker import check_node
+
+    with patch("asyncio.create_subprocess_exec") as mock_exec:
+        result = await check_node("ping", "-O", None)
+
+    mock_exec.assert_not_called()
+    assert result["status"] == "unknown"
+
+
+@pytest.mark.asyncio
+async def test_check_node_rejects_flag_like_ip():
+    from app.services.status_checker import check_node
+
+    with patch("asyncio.create_subprocess_exec") as mock_exec:
+        result = await check_node("ping", None, "-O")
+
+    mock_exec.assert_not_called()
+    assert result["status"] == "unknown"
+
+
 # --- _tcp_connect ---
 
 @pytest.mark.asyncio