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GHSA-m6vc-f87m-cc2h

MediumCVSS 6.3 / 10
Published Jun 4, 2026·Last modified Jun 4, 2026
Affected Components(0)

No affected components available

Description

Impact

The DynamicClientRegistrationController#register action hard-codes confidential: false when creating applications (dynamic_client_registration_controller.rb:18-25), yet the response includes a client_secret and advertises token_endpoint_auth_methods_supported: ["client_secret_basic", "client_secret_post"].

Because Doorkeeper's Application.by_uid_and_secret treats a blank/missing secret as valid for non-confidential (public) clients, an attacker who knows only the client_id (which is public information) can authenticate as the dynamically-registered client at the token endpoint.

Note that Dynamic Client Registration is opt-in feature which is disabled by default so only projects that explicitly enabled it are affected.

Steps to Reproduce

  1. Enable dynamic client registration in the initializer
  2. POST /oauth/registration with client_name, redirect_uris, and scope
  3. Observe: response returns client_secret, but the created Doorkeeper::Application has confidential: false
  4. Call Doorkeeper::Application.by_uid_and_secret(client_id, nil) — it returns the application (credentials bypass)
  5. POST /oauth/token with grant_type=client_credentials and only client_id (no client_secret) — the token endpoint issues an access token without any secret verification

Patches

Patched in 1.10.0

Workarounds

Upgrade existing applications created with a Dynamic Client registration to have confidential: true

Risk Scores
Base Score
6.3

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
1.7

Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.

EPSS
N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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Medium severity
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