CVE-2026-73563 @backstage/plugin-auth-backend: Unauthenticated OAuth account takeover via `redirect_uri` allowlist bypass
Attackers can bypass OAuth redirect URI allowlists in experimental Backstage auth features to steal authorization codes and take over accounts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-73563?
CVE-2026-73563 is a medium-severity vulnerability in backstage, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Backstage is an open framework for building developer portals. Prior to 0.29.2, the experimental dynamic client registration and client ID metadata document features in the @backstage/plugin-auth-backend use full-string matcher.isMatch glob matching for auth.experimentalDynamicClientRegistration.allowedRedirectUriPatterns and the auth.experimentalClientIdMetadataDocuments allowedClientIdPatterns and allowedRedirectUriPatterns options. A hostname wildcard can match across URL component boundaries, allowing an attacker-controlled redirect URI with a trusted hostname suffix in its path to pass the allowlist and receive an OAuth authorization code after a victim completes the flow. Patterns without an explicit protocol can match unintended protocols, and redirect URIs containing embedded credentials are accepted after user information is stripped for matching. The features are experimental and disabled by default; only deployments that enable them and configure custom wildcard-hostname or protocol-less patterns are affected. This issue is first fixed in prerelease version 0.29.2.
Weakness: CWE-601
Which versions are affected by CVE-2026-73563?
2 open source packages ship an affected version, including @backstage/plugin-auth-backend. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
@backstage/plugin-auth-backend npm | All versions | 0.29.2 |
@backstage/plugin-auth-backend npm | All versions | 0.29.2 |
Products include Linuxfoundation Backstage\/Plugin-Auth-Backend.
How do I fix CVE-2026-73563?
Upgrade @backstage/plugin-auth-backend to 0.29.2 or later.
Is CVE-2026-73563 being exploited?
There is no known exploitation of CVE-2026-73563 in the wild and no public exploit code.
Sources
Also known as GHSA-38hq-7x33-php4.