The provided reference URLs contain CSAF advisories and a CISA advisory page. These documents describe the vulnerability (CVE-2026-76943) in Xiiaozet LK100W as an 'authentication weakness within an administrative service' that allows an attacker to 'bypass intended access controls and obtain command execution capabilities'. The affected product version is stated as '<2.1.240', and the remediation is to update to v2.1.240. However, these advisories do not include any specific technical details such as commit hashes, file paths, or function names that were modified or are directly responsible for the vulnerability. Without access to the source code or detailed patch information, it is impossible to pinpoint the exact functions that constitute the 'authentication weakness' or the 'administrative service' involved in the bypass. Therefore, no specific vulnerable functions can be identified with high confidence.