OpenStack Keystone provides authentication, authorization, and service discovery for OpenStack. Grzegorz Grasza (Red Hat) and Tim Shephard (roiai.ca) independently identified that Keystone does not consistently enforce scope restrictions on tokens obtained via delegated authentication methods.

This flaw covers Launchpad #2158538 (token reauthentication escape). token_authenticate() in keystone/auth/plugins/token.py only blocked application_credential tokens from rescoping when an explicit scope was requested. Omitting scope caused the new token to fall through to the user's default project, escaping the application credential's project binding. EC2 credential tokens matched no delegation check at all and could rescope to any project where the underlying user has role assignments.

An attacker with a limited-scope application credential or EC2 credential can exchange it via POST /v3/auth/tokens (token method) for a token scoped to a different project, gaining access beyond the original credential's intended project scope.

Upstream affected range: Keystone >=25.0.0 through unfixed 27.x, 28.x, and 29.x releases. Proposed patches add a _PRIMARY_AUTH_METHODS allowlist and reject delegated tokens from the token-method reauthentication path entirely. No compensating control was found for the application-credential default-project escape on stable or master.

CVE IDs have been requested by the OpenStack Vulnerability Management Team and are not yet assigned (CVE-2026-pending).
Reporter: Grzegorz Grasza (Red Hat) and Tim Shephard (roiai.ca). Coordinated by Goutham Pacha Ravi, OpenStack VMT.
Private Launchpad report: https://launchpad.net/bugs/2158538
PSIRT Ticket: PSIRTSUPT-21454