Backstage up to 0.29.1 Dynamic Client Registration redirect

Summaryinfo

A vulnerability labeled as problematic has been found in Backstage up to 0.29.1. This impacts an unknown function of the component Dynamic Client Registration. Executing a manipulation of the argument auth.experimentalDynamicClientRegistration.allowedRedirectUriPatterns/auth.experimentalClientIdMetadataDocuments.allowedClientIdPatterns/auth.experimentalClientIdMetadataDocuments.allowedRedirectUriPatterns can lead to redirect. This vulnerability appears as CVE-2026-73563. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as problematic was found in Backstage up to 0.29.1. This vulnerability affects an unknown part of the component Dynamic Client Registration. The manipulation of the argument auth.experimentalDynamicClientRegistration.allowedRedirectUriPatterns/auth.experimentalClientIdMetadataDocuments.allowedClientIdPatterns/auth.experimentalClientIdMetadataDocuments.allowedRedirectUriPatterns with an unknown input leads to a redirect vulnerability. The CWE definition for the vulnerability is CWE-601. A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks. As an impact it is known to affect integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-73563 since 08/12/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1204.001.

Upgrading to version 0.29.2 eliminates this vulnerability.

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Productinfo

Name

• Backstage

Version

• 0.29.0
• 0.29.1

Website

• Product: https://github.com/backstage/backstage/

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