New research into Zyxel's credential management has revealed a catastrophic failure in cryptographic entropy, transforming a localized bug into a global infrastructure risk. What began as a credential leak in a single VMG3625-T50B router image (CVE-2021-35036) has been expanded by OSINT researchers to include a wide array of CPE, ONT, LTE, and 5G devices. The core of the issue is not merely that passwords exist in configuration files, but that Zyxel's 'supervisor' and 'admin' credentials are generated using a deterministic algorithm that can be reverse-engineered. By running Zyxel’s own password generator under QEMU emulation, researchers were able to trace the routines used to create management secrets. This means that an attacker with knowledge of a device's MAC address or serial number can potentially calculate the administrative password without ever touching the device. Furthermore, low-privileged sessions can reach backend DAL endpoints that return supervisor account data, FTPS credentials, and TR-069 management secrets. This effectively grants an attacker full remote management capability over critical internet gateway infrastructure. The impact is particularly severe for telecommunications providers, as TR-069 is the standard protocol used for remote configuration of millions of home and business routers. If these management secrets are compromised at scale, threat actors could redirect DNS traffic, perform man-in-the-middle attacks, or enlist millions of devices into a global botnet. This discovery highlights the 'Hardware Debt' crisis, where legacy code in embedded systems remains a persistent threat long after the initial vulnerabilities are identified. Organizations and ISPs must move beyond simple firmware updates and implement network-level isolation for management interfaces, ensuring that DAL endpoints and TR-069 services are never exposed to the public internet. The Zyxel case serves as a stark reminder that 'security through obscurity'—especially when relying on deterministic algorithms—is a recipe for structural collapse in the face of modern firmware analysis tools.