The loginWithMailLink endpoint returns a full authentication URL that contains an authentication token in the HTTP response body when the login_with_mail_link_enable feature is active. An unauthenticated attacker can submit a known email address to this endpoint and receive a complete login URL. By sending that URL to the token2Login endpoint, the attacker obtains a bearer token that grants full account access, including administrative privileges. The flaw is a direct information‑exposure weakness (CWE‑201).

Versions of cedar2025 Xboard from 0.1.0 through 0.1.9 and v2board from 1.6.1 through 1.7.4 are affected when the login_with_mail_link_enable feature is enabled.

The CVSS base score of 9.1 marks the vulnerability as critical. An attacker can exploit it from any network location by simply POSTing a known email address to the loginWithMailLink endpoint; no authentication, special permissions, or code execution are required. EPSS data is not available, and the vulnerability is not listed in the CISA KEV catalog, but the lack of exposure controls and the ease of obtaining valid tokens make the risk immediate and high.