Manager-io/Manager is accounting software. In Manager Desktop and Server versions 25.11.1.3085 and below, a critical vulnerability permits unauthorized access to internal network resources. The flaw lies in the fundamental design of the DNS validation mechanism. A Time-of-Check Time-of-Use (TOCTOU) condition that allows attackers to bypass network isolation and access internal services, cloud metadata endpoints, and protected network segments. The Desktop edition requires no authentication; the Server edition requires only standard authentication. This issue is fixed in version 25.11.1.3086.