A critical authentication bypass vulnerability in SiYuan allows unauthenticated remote attackers to brute-force administrative access codes, potentially leading to a full system compromise.

The application fails to restrict excessive authentication attempts within the CheckAuth middleware for the HTTP Basic Authentication branch. This flaw allows unauthenticated attackers to perform unlimited brute-force attempts to guess the workspace access code and gain administrative privileges.

Successful exploitation grants an attacker full RoleAdministrator access to the application kernel. This level of access poses a severe risk of unauthorized data modification, total loss of confidentiality, and potential disruption of business operations, justifying the critical CVSS score of 9.8.

Immediate Action: Update the SiYuan software to version 3.7.4 or later to implement proper authentication rate limiting.

Proactive Monitoring: Review system access logs for high volumes of failed authentication attempts targeting the /api/* endpoints.

Compensating Controls: Implement network-level rate limiting or an IP-based blocklist via a Web Application Firewall to restrict automated brute-force traffic.

Public Exploit Available: No (exploit_available: false)

Given the ease of exploitation and the high level of access granted, this vulnerability presents an immediate risk to any exposed SiYuan instance. Organizations must prioritize updating to version 3.7.4 immediately to remediate the authentication bypass and prevent unauthorized administrative access.