CVE-2026-53728 - Medplum - Improper Validation of Redirect URI in External Auth Callback allows Authorization Code Leakage
Brief
CVE ID : CVE-2026-53728
Published : Sept. 3, 2026, 8:17 p. m.
- 23 minutes ago
Description : Medplum is a developer platform that enables development of healthcare apps. Prior to version 5.
- 6, the external identity provider callback at GET /auth/external accepts attacker-controlled redirect URIs that only need to start with a registered client redirect URI, rather than matching exactly.
After a successful external IdP login, the server appends Medplum login and code values to that attacker-supplied URL and issues a redirect. Because the external login request state is serialized as raw JSON and later trusted by the callback, an attacker who can tamper with state. redirectUri can cause Medplum to redirect authorization artifacts to an attacker-controlled endpoint.