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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-53728
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-03 20:17:21 UTC
Updated2026-09-09 21:09:13 UTC
DescriptionMedplum 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.

Risk And Classification

Primary CVSS: v3.1 7.1 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L

EPSS: 0.001380000 probability, percentile 0.035280000 (date 2026-09-10)

Problem Types: CWE-345 | CWE-601 | CWE-601 CWE-601: URL Redirection to Untrusted Site ('Open Redirect') | CWE-345 CWE-345: Insufficient Verification of Data Authenticity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L
3.1CNADECLARED7.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Medplum Medplum affected < 5.1.6 Not specified

References

ReferenceSourceLinkTags
github.com/medplum/medplum/releases/tag/v5.1.6 [email protected] github.com
github.com/medplum/medplum/pull/8749 [email protected] github.com
github.com/medplum/medplum/commit/7ae10035ddadde4dba7b18d3156553940465b3a1 [email protected] github.com
github.com/medplum/medplum/security/advisories/GHSA-m44r-7c5h-m6mj 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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