The LDAP authentication endpoint in Open WebUI, before version 0.9.0, does not enforce a non‑empty password before attempting a Simple Bind. An attacker can send an empty password string, which the Pydantic model accepts, and the bind succeeds on vulnerable LDAP servers. The application then issues a fully valid session token for the chosen user. This flaw is classified as CWE‑287 and allows an unauthorized user to obtain access as any known LDAP account.

All instances of Open WebUI older than 0.9.0 that use LDAP authentication through the exposed endpoint are vulnerable. The issue resides in the open‑webui product distributed by the maintainer. Any deployment relying on LDAP for login is susceptible.

The vulnerability has a CVSS score of 9.1 and an EPSS score of 3%, indicating a low but non‑zero probability that it will be exploited in the wild. The flaw is not listed in the CISA KEV catalog. The likely attack vector is remote: a client that can reach the web host can submit an HTTP request to the LDAP endpoint with an empty password and obtain a valid session token for any existing LDAP user, thereby gaining the privileges of that user.