Open WebUI LDAP Empty Password Authentication Bypass Vulnerability

A critical vulnerability exists in Open WebUI versions prior to 0.9.0, allowing an authentication bypass via the LDAP authentication endpoint. The issue arises because the endpoint does not verify that the submitted password is non-empty before executing a Simple Bind against the LDAP server. The LdapForm Pydantic model permits empty strings as valid passwords, enabling the Connection.bind() call to succeed on vulnerable LDAP servers. This flaw results in the application issuing a full session token for the user, granting access to their account. The vulnerability affects all versions with LDAP authentication support, including the current main branch.

Impact

Exploitation of this vulnerability leads to a complete authentication bypass, allowing any LDAP user account to be accessed without knowledge of the password. This includes administrative accounts that authenticate via LDAP. The vulnerability also bypasses rate limiting, unlike the standard password sign-in process.

Reproduction

To reproduce this vulnerability, ensure that LDAP authentication is enabled on the Open WebUI instance and that the LDAP server accepts unauthenticated simple binds with empty passwords. Then, send a POST request to the LDAP authentication endpoint with a valid username and an empty password. The server will respond with a success status, and the application will issue a session token for the user, granting access to their account.

Remediation

Users can upgrade to Open WebUI version 0.9.0 or later, where this vulnerability has been fixed.