PyPI · open-webui
Open WebUI: Account enumeration via observable login timing discrepancy
The /api/v1/auths/signin endpoint leaked whether an email address belonged to a registered account through a response-time side channel. Password verification ran bcrypt only when the email was found in the database; for a non-existent email the request returned early without hashing. The expensive bcrypt comparison therefore made valid-account attempts respond significantly slower (180 ms) than non-existent ones (5 ms), so an unauthenticated attacker could enumerate valid accounts by measuring response time.
On signin the backend looked the user up by email and only performed the bcrypt password comparison if a record existed. A missing email short-circuited before any hashing, producing the timing gap. The built-in brute-force throttling did not prevent it: sending one request at a time with a small delay between requests stays under the rate limit while still exposing the difference.
Observed in the reporter's run (HTTP 400 for every attempt, the response time is the signal):
Email Status Response time
joe@example.com 400 186 ms <- valid account
larry@example.com 400 9 ms
jose@example.com 400 6 ms
james@example.com 400 5 ms
An unauthenticated attacker can enumerate which email addresses are registered accounts, which enables targeted password-spraying against confirmed accounts. The impact is amplified by MFA not being enabled by default. No data is read or modified; the disclosure is limited to account existence.
The authentication path now runs a bcrypt verification against a constant placeholder hash whenever the email does not resolve to an active credential, so a real hash comparison executes on every attempt and the response time is the same whether or not the account exists. Fixed in 0.10.0.
@dievus
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