CVE-2026-45339: Open WebUI: API key endpoint restrictions bypassed via `x-api-key` header — full message processing on restricted endpoints

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-15 · updated 2026-06-17
Weakness: CWE-863

Description

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.0, Open WebUI allows admins to restrict which API endpoints an API key can access. When an API key is restricted from /api/v1/messages, requests using the Authorization: Bearer sk-... header are correctly blocked with 403. However, the same key sent via the x-api-key header bypasses the restriction entirely — the request is authenticated, the model is invoked, and a full response is returned. This vulnerability is fixed in 0.9.0.

Affected products

open-webui: before 0.9.0 — fixed in 0.9.0

How to fix

Upgrade to a fixed version: open-webui 0.9.0. Check the vendor advisory for mitigations.

References

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