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GHSA-q333-f498-w2x7
@backstage/plugin-auth-backend-module-cloudflare-access-providerImpact
The Cloudflare Access auth provider verifies a token's signature and team issuer, but affected versions do not verify that the token was issued for the Backstage application. A user holding a valid token for another Access application in the same Cloudflare Zero Trust team may therefore be able to authenticate to Backstage if that token reaches the auth endpoint without the Backstage application's audience already being enforced upstream.
Cloudflare Access normally evaluates the protected application before forwarding requests. The reported reproduction exercises the provider directly and does not demonstrate bypass through the ordinary Cloudflare-protected Backstage URL. Relevant deployment topologies include direct origin access, alternate routes around the intended Access application, or another proxy forwarding the assertion unchanged.
A successful sign-in also depends on the deployment's sign-in resolver mapping the presented identity to a Backstage user. The resulting impact depends on the permissions assigned to that identity.
Patches
Upgrade @backstage/plugin-auth-backend-module-cloudflare-access-provider to version 0.5.0 or later. The fixed package is available in Backstage v1.55.0.
This is a breaking configuration change. Before upgrading, set auth.providers.cfaccess.audience to the Audience (AUD) tag for the Backstage application in Cloudflare Zero Trust:
auth:
providers:
cfaccess:
teamName: example
audience: ${AUTH_CFACCESS_AUDIENCE}
Workarounds
- Restrict access to the Backstage auth endpoint to the intended Cloudflare Access application.
- Use a custom authenticator that validates the application audience.
- Disable the provider until the patched package can be deployed.
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The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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