The LDAP authentication endpoint in Open WebUI, prior to version 0.9.0, fails to enforce a non‑empty password before performing a Simple Bind. An attacker can submit an empty string, which the Pydantic model accepts, and the subsequent bind succeeds against vulnerable LDAP servers. The application then issues a valid session token for the targeted user. This flaw, classified as CWE‑287, permits unauthorized users to obtain access to the platform as any account whose LDAP entry is known.

Versions of Open WebUI earlier than 0.9.0 are affected. The flaw resides in the Open WebUI open‑webui product and affects all deployments that use LDAP authentication through the exposed endpoint.

The vulnerability carries a CVSS score of 9.1 and is not listed in the CISA KEV catalog. No EPSS score is available, so the exact exploitation probability is unknown. The likely attack vector is remote: a client able to reach the web host can send an HTTP request to the LDAP endpoint with an empty password, exploiting the lack of validation to obtain a full session token for any existing LDAP user. Once authenticated, the attacker gains access with the privileges of that user.