Open WebUI: Account enumeration via observable login timing discrepancy
Medium5.3CVE-2026-59218 · Published Jul 24, 2026 · updated Aug 4, 2026
### Summary 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. ### Details 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 ...
Affected versions
| Package | Affected | Fixed in |
|---|---|---|
| open-webui PyPI | < 0.10.0 | 0.10.0 |
Details and references
### Summary 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. ### Details 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 ``` ### Impact 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. ### Patched 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. ### Credits @dievus
- CVSS 3.1
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- Severity from
- GitHub (reviewed advisory)
- Weakness
- CWE-208
- Also known as
- CVE-2026-59218, PYSEC-2026-3594
- github.com/open-webui/open-webui/security/advisories/GHSA-7rw5-9f7q-xj36
- nvd.nist.gov/vuln/detail/CVE-2026-59218
- github.com/open-webui/open-webui/pull/26385
- github.com/open-webui/open-webui/commit/993e74912199c66c522f08ec81abe31d76985e39
- github.com/open-webui/open-webui
- github.com/open-webui/open-webui/releases/tag/v0.10.0
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