Craft CMS versions 4.0.0-RC1 through before 4.18.2 and 5.0.0-RC1 through before 5.10.6 contain a vulnerability where authenticated users with control panel access can leak secret environment variables. This occurs because environment variables are interpolated into Twig templates even when the Twig sandbox is enabled, allowing secrets to be extracted via blind error-based techniques. The vulnerability enables attackers to incrementally exfiltrate sensitive secrets such as the CRAFT_SECURITY_KEY, database credentials, and API keys, potentially leading to session forgery and privilege escalation.