CVE-2026-53728
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.14%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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. 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. When the registered redirect URI is a bare origin or another prefix that can be extended into a different hostname, this becomes a cross-origin authorization code leak. This issue has been patched in version 5.1.6.
- CVSS 3.1
- 7.1 HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L
- EPSS
- 0.14% probability · 4th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-345, CWE-601
- Source
- security-advisories@github.com
References
- https://github.com/medplum/medplum/commit/7ae10035ddadde4dba7b18d3156553940465b3a1
- https://github.com/medplum/medplum/pull/8749
- https://github.com/medplum/medplum/releases/tag/v5.1.6
- https://github.com/medplum/medplum/security/advisories/GHSA-m44r-7c5h-m6mj
- https://github.com/medplum/medplum/security/advisories/GHSA-m44r-7c5h-m6mj
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.