CVE-2026-45675: Open WebUI: TOCTOU race grants admin on first OAuth/LDAP

## Summary The LDAP and OAuth authentication flows use a TOCTOU (Time-of-Check-Time-of-Use) pattern for first-user admin role assignment. The regular signup handler (`signup_handler` in auths.py, line 663) was explicitly patched to prevent this race with the comment *"Insert with default role first to avoid TOCTOU race"*, but the LDAP and OAuth code paths were never updated with the same fix. ## Vulnerable Code ### LDAP (auths.py, lines 479-490) ```python # Line 482 - CHECK: is the user table empty? role = 'admin' if not Users.has_users(db=db) else request.app.state.config.DEFAULT_USER_ROLE # Lines 484-490 - USE: create user with the role determined above user = Auths.insert_new_auth( email=email, password=str(uuid.uuid4()), name=cn, role=role, # <-- role was determined BEFORE insert, race window exists db=db, ) ``` ### OAuth (oauth.py, lines 1103-1112, 1566-1574) ```python # Line 1104 - CHECK: count users def get_user_role(self, user, user_data): user_count = Users.get_num_users() if not user and user_count == 0: return 'admin' # Line 1112 # Lines 1566-1574 - USE: create user with pre-determined role user = Auths.insert_new_auth( ... role=self.get_user_role(None, user_data), # Line 1571 ... ) ``` Both paths determine the role BEFORE inserting the user, creating a race window where multiple concurrent requests on a fresh instance can all observe an empty database and all receive the `admin` role. ## Comparison with Patched Signup The `signup_handler` (auths.py, line 663) was explicitly fixed: ```python # Insert with default role first to avoid TOCTOU race user = Auths.insert_new_auth(..., role=DEFAULT_USER_ROLE, ...) # Then check if this is the only user and upgrade if Users.get_num_users() == 1: Users.update_user_role_by_id(user.id, 'admin') ``` The LDAP and OAuth paths did NOT receive this fix. ## Exploitation 1. Deploy Open WebUI with LDAP or OAuth enabled on a fresh instance (no existing users) 2. Send multiple concurrent authentication requests from different users 3. Multiple requests pass the `has_users()` / `get_num_users() == 0` check simultaneously 4. All concurrent users become administrators `DATABASE_ENABLE_SESSION_SHARING` defaults to `False` (env.py:387), so each call uses its own database session, widening the race window. ## Impact Any LDAP/OAuth user who times their first login concurrently with the legitimate first admin can escalate to full admin privileges, gaining access to all user data, system configuration, API keys, and connected LLM backends. ## Suggested Fix Apply the same insert-then-check pattern used in `signup_handler`: insert the user with `DEFAULT_USER_ROLE` first, then atomically check if this is the only user and upgrade to admin only if so. ## Resolution Fixed in PR [#23626](https://github.com/open-webui/open-webui/pull/23626) (commit [96a0b3239](https://github.com/open-webui/open-webui/commit/96a0b3239b1aadb23fc359bf10849c9ba12fd6ec)), first released in **v0.9.0** (Apr 2026). Both LDAP (`routers/auths.py`) and OAuth (`utils/oauth.py`) registration paths now use the same insert-first-check-after pattern that `signup_handler` already had: 1. Insert the new user with `DEFAULT_USER_ROLE` unconditionally — no pre-insert role decision based on user count. 2. After the insert commits, atomically call `Users.get_num_users() == 1` to check whether this is the sole user. 3. Only the sole user gets promoted to `admin` via `Users.update_user_role_by_id`. `OAuthManager.get_user_role` was also updated to return `DEFAULT_USER_ROLE` (not `admin`) for first-user bootstrap; admin promotion is deferred to the post-insert check above. With this ordering, two concurrent first-user registrations that both observe an empty table can both insert, but only one will see `get_num_users() == 1` afterward — the other will see `== 2` and not be promoted. Users on `>= 0.9.0` are not affected.

An adversary identifies a target organization deploying Open WebUI with LDAP integration via job postings, tech stack reconnaissance, or internal network scanning. During the brief onboarding window when the legitimate first admin is configuring the fresh instance, the adversary simultaneously sends multiple concurrent LDAP authentication requests from different accounts they control. All requests hit Users.has_users() before any user record is committed — all observe an empty database and all are assigned the admin role by the pre-insert role decision logic. The adversary's accounts now have persistent admin access to the LLM gateway: they extract all stored API keys for OpenAI and Anthropic, read complete user conversation histories, inject malicious system prompts affecting all subsequent users, and create additional backdoor admin accounts before the legitimate admin notices unexpected entries in the user list.