CVE-2026-32235
MEDIUM5.9EPSS 0.03%@backstage/plugin-auth-backend: OAuth redirect URI allowlist bypass
Description
### Impact 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. ### Patches Upgrade to `@backstage/plugin-auth-backend` version 0.27.1 or later. ### Workarounds Disable experimental Dynamic Client Registration and Client ID Metadata Documents features if they are not required. ### References - [RFC 6749 Section 3.1.2 - Redirection Endpoint](https://datatracker.ietf.org/doc/html/rfc6749#section-3.1.2)
Affected packages (1)
- npm/@backstage/plugin-auth-backendfrom 0, < 0.27.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N |