A08 Software or Data Integrity Failures

import pickle, base64

def load_prefs(cookie):
    return pickle.loads(base64.b64decode(cookie))   # attacker-controlled bytes run code

const cart = JSON.parse(Buffer.from(req.cookies.cart, "base64").toString());
total = cart.total;          // the client wrote this number

<script src="https://cdn.example.com/lib/chart.min.js"></script>

import hmac, hashlib, json, base64

SECRET = load_secret("PREFS_HMAC_KEY")

def dump_prefs(prefs: dict) -> str:
    body = base64.urlsafe_b64encode(json.dumps(prefs).encode())
    mac = hmac.new(SECRET, body, hashlib.sha256).hexdigest().encode()
    return (body + b"." + mac).decode()

def load_prefs(cookie: str) -> dict:
    body, _, mac = cookie.encode().partition(b".")
    expected = hmac.new(SECRET, body, hashlib.sha256).hexdigest().encode()
    if not hmac.compare_digest(mac, expected):
        raise ValueError("tampered")
    return json.loads(base64.urlsafe_b64decode(body))      # data only, validated after

// state lives on the server; the cookie only carries an opaque id
const cart = await carts.get(req.session.cartId);
const total = cart.items.reduce((s, i) => s + catalog.price(i.sku) * i.qty, 0);

<script src="https://cdn.example.com/lib/chart-4.4.1.min.js"
        integrity="sha384-<hash of the exact file>"
        crossorigin="anonymous"></script>

# the artifact must be signed by the expected pipeline identity
cosign verify-blob --certificate-identity 'https://github.com/example/app/.github/workflows/release.yml@refs/heads/main' \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  --signature app.tgz.sig --certificate app.tgz.pem app.tgz

def test_tampered_cookie_is_rejected():
    cookie = dump_prefs({"theme": "dark"})
    body, mac = cookie.split(".")
    forged = base64.urlsafe_b64encode(b'{"theme":"dark","role":"admin"}').decode() + "." + mac
    with pytest.raises(ValueError):
        load_prefs(forged)

def test_pickle_payload_is_not_executed(tmp_path):
    marker = tmp_path / "pwned"
    class Evil:
        def __reduce__(self):
            return (open, (str(marker), "w"))
    payload = base64.b64encode(pickle.dumps(Evil())).decode()
    with pytest.raises(Exception):
        load_prefs(payload)
    assert not marker.exists()

# every external <script> and <link rel=stylesheet> must carry an integrity attribute
! grep -RInE '<script[^>]+src="https?://' dist/ | grep -v 'integrity='