CVE-2026-73056 in SiYuan
Summary
by MITRE • 08/16/2026
SiYuan kernel versions before 3.7.4 contain an improper restriction of excessive authentication attempts vulnerability in the CheckAuth() middleware. The middleware accepts the API token (Conf.Api.Token) via an Authorization header (Token/Bearer) or a ?token= query parameter, and neither path is protected by the application's CAPTCHA/lockout mechanism (NeedCaptcha/WrongAuthCount). As a result, an unauthenticated remote attacker can perform unlimited automated guesses of the API token, particularly when a short or weak custom token has been configured, and upon success gains full RoleAdministrator access enabling arbitrary file operations and SQL queries.
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Analysis
by VulDB Data Team • 08/16/2026
The vulnerability identified in SiYuan kernel versions prior to 3.7.4 represents a critical authentication bypass resulting from an improper restriction of excessive authentication attempts within the CheckAuth middleware. This flaw fundamentally undermines the integrity of the application's access control mechanisms by allowing unauthenticated remote attackers to perform unlimited automated guessing attacks against API tokens. The technical root cause lies in the dual acceptance paths for credential validation, where the system accepts API tokens either through a standard Authorization header using Token or Bearer schemes or via a query parameter named token. Crucially, neither of these input vectors is subjected to the application's intended rate-limiting and lockout protections, specifically the NeedCaptcha mechanism which triggers CAPTCHA challenges after repeated failures, nor the WrongAuthCount logic that should enforce account locks following excessive incorrect attempts. This architectural oversight creates a significant blind spot in security monitoring and enforcement, allowing attackers to bypass standard brute-force mitigation strategies entirely.
From an operational perspective, this vulnerability enables severe consequences for system integrity and data confidentiality. An attacker can leverage automated scripts to rapidly iterate through potential API token values with no throttling or blocking mechanisms in place. This is particularly dangerous when administrators have configured short or weak custom tokens, as the search space becomes computationally trivial to exhaust within a short timeframe. Once an attacker successfully guesses a valid API token, they are granted full RoleAdministrator privileges without any further authentication hurdles. This elevation of privilege allows for arbitrary file operations across the system and unrestricted SQL query execution against the underlying database. Such capabilities effectively result in complete system compromise, enabling data exfiltration, modification of critical configuration files, or potential remote code execution depending on the specific environment configurations and available attack vectors within the administrative interface.
This vulnerability aligns with CWE-307 Improper Restriction of Excessive Authentication Attempts, as it fails to enforce appropriate limits on authentication requests from a single source. Furthermore, the exploitation path corresponds to ATT&CK technique T1110 Brute Force, specifically highlighting how attackers can bypass rate-limiting controls when they are not uniformly applied across all authentication entry points. The lack of consistent enforcement for both header-based and query-string based token validation demonstrates a failure in implementing defense-in-depth principles regarding credential verification processes.
To mitigate this vulnerability, immediate updates to the SiYuan kernel version 3.7.4 or later are required as these versions address the logic flaws within the CheckAuth middleware. In environments where upgrading is not immediately feasible, administrators should implement network-level rate limiting using firewalls or reverse proxies to restrict the frequency of requests targeting authentication endpoints regardless of the input method used. Additionally enforcing strong complexity requirements for API tokens significantly increases the computational cost required for successful guessing attacks. It is also recommended to review and harden all authentication entry points to ensure that CAPTCHA challenges and lockout mechanisms are consistently applied across every possible vector for credential submission, thereby closing the gap exploited by this specific implementation flaw.