Hatchet is a platform for orchestrating background tasks, AI agents, and durable workflows at scale. Prior to 0.91.1, ValidateOAuthState clears the oauth_state_ session value to an empty string after a successful OAuth callback and later accepts an empty state parameter as equal, allowing an unauthenticated attacker to bind a victim's Hatchet session to an attacker-controlled OAuth identity. Exploitation requires the victim to have completed an OAuth flow in the current session and the deployment to enable auth.google.enabled, auth.github.enabled, or the Slack integration. This issue is fixed in version 0.91.1.