HyperCloud versions 2.3.5 through 2.6.8 improperly allowed refresh tokens to be used directly for resource access and failed to invalidate previously issued access tokens when a refresh token was used. Because refresh tokens have a significantly longer lifetime (default one year), an authenticated client could use a refresh token in place of an access token to maintain long-term access without token rotation. Additionally, old access tokens remained valid after refresh, enabling concurrent or extended use beyond intended session boundaries. This vulnerability could allow prolonged unauthorized access if a token is disclosed.