| Package | Affected versions | Patched versions |
|---|---|---|
| backstage | ≤ 0.27.0 | |
| @backstage/plugin-auth-backend | < 0.27.1 | 0.27.1 |
The experimental OIDC provider in @backstage/plugin-auth-backend is vulnerable to a redirect URI allowlist bypass. Instances that have enabled experimental Dynamic Client Registration or Client ID Metadata Documents and configured allowedRedirectUriPatterns are affected.
A specially crafted redirect URI can pass the allowlist validation while resolving to an attacker-controlled host. If a victim approves the resulting OAuth consent request, their authorization code is sent to the attacker, who can exchange it for a valid access token.
This requires victim interaction and that one of the experimental features is explicitly enabled, which is not the default.
Upgrade to @backstage/plugin-auth-backend version 0.27.1 or later.
Disable experimental Dynamic Client Registration and Client ID Metadata Documents features if they are not required.
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