CVE-2026-53728 Medplum - Improper Validation of Redirect URI in External Auth Callback allows Authorization Code Leakage

Medplum is a developer platform that enables development of healthcare apps. Prior to version 5.1.6, 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...

CVE-2026-53728

Medplum , a healthcare developer platform, is vulnerable to authorization code leakage in its external identity provider callback (GET /auth/external). The root cause is that getClientRedirectUri() accepts any redirect URI that prefix-matches a registered value (startsWith), rather than requiring...

GHSA-M44R-7C5H-M6MJ Medplum: Improper Validation of Redirect URI in External Auth Callback allows Authorization Code Leakage

Summary 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...