CVE-2026-45339: Open WebUI authorization bypass via x-api-key header

Executive brief

Open WebUI, a popular interface for interacting with large language models, contains a flaw that allows users to bypass restrictions placed on their API keys. While administrators can limit which features an API key can access, a user can circumvent these rules by using a specific alternative header in their web requests. This could allow unauthorized users to access administrative functions or use expensive AI resources that were intended to be restricted.

Technical details

An incorrect authorization vulnerability (CWE-863) exists in Open WebUI where endpoint restriction checks are only applied to API keys provided via the 'Authorization: Bearer' header. The application's Anthropic-compatible API path also accepts the 'x-api-key' header, but fails to trigger the restriction validation logic for this header. An attacker with a valid but restricted API key can bypass these restrictions to access any API endpoint, including chat completions and potentially administrative functions. This issue is fixed in version 0.9.0.

Affected products

• Open WebUI open-webui <= 0.8.12

Timeline

• 2026-05-09: patched: Version 0.9.0 released
• 2026-05-14: advisory: GitHub Advisory published

References

• https://api.github.com/users/aliceQWAS
• https://github.com/aliceQWAS
• https://api.github.com/users/aliceQWAS/gists%7B/gist_id%7D
• https://api.github.com/users/aliceQWAS/repos
• https://avatars.githubusercontent.com/u/268486471?v=4
• https://api.github.com/users/aliceQWAS/events%7B/privacy%7D