CVE-2026-53728Public exploitNetwork attack vectorHinoki check available

Account takeover via prefix-matched redirect URI

Published Sep 3, 2026 · Updated Sep 3, 2026

Open redirect in Medplum before 5.1.6 allows remote attackers to steal authorization codes and take over accounts during external IdP login. The unauthenticated GET /auth/external callback trusts raw JSON state and accepts state.redirectUri when it only starts with a registered URI, then appends login and code values to that URL. Exploitation requires a configured external identity provider, a prefix-extensible registered redirect URI, and a victim who completes the login flow; the stolen code can be redeemed with attacker-chosen PKCE values for the victim's session.

CVSS severity7.1
High
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Open redirect in Medplum before 5.1.6 allows remote attackers to steal authorization codes and take over accounts during external IdP login. The unauthenticated GET /auth/external callback trusts raw JSON state and accepts state.redirectUri when it only starts with a registered URI, then appends login and code values to that URL. Exploitation requires a configured external identity provider, a prefix-extensible registered redirect URI, and a victim who completes the login flow; the stolen code can be redeemed with attacker-chosen PKCE values for the victim's session.

The record

CVE
CVE-2026-53728
Published
Sep 3, 2026
Updated
Sep 3, 2026
Vendor
Medplum
Product
Medplum
Classifications
CWE-345, CWE-601, T1528, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 5.1.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Medplum · Medplumversion=< 5.1.6

Published CVSS scores

7.1GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-345Insufficient Verification of Data Authenticity
CWE-601URL Redirection to Untrusted Site ('Open Redirect')
T1528Steal Application Access Token
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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