CVE-2026-106460: Backstage: Explicit negative email verification can be ignored during shared OAuth profile normalization

Several Passport-based authentication providers use shared OAuth profile normalization from @backstage/plugin-auth-node. Affected versions may pass an email to email-based sign-in resolvers even when verification metadata supplied for that same address is explicitly negative. The ID-token-only fallback likewise did not consistently respect email_verified: false.

Exploitation requires a deployment where an admitted identity-provider user can supply or change an email address without verification and Backstage uses that profile email to resolve catalog identities. In that configuration, the user may be able to assume another catalog identity and obtain its associated access and permissions.

An absent email_verified claim is not by itself considered an affected condition. Some providers rely on authoritative organizational provisioning and intentionally omit the optional claim. Operators using email-based sign-in resolution must ensure that the configured provider restricts sign-in to the intended user population and supplies an authoritative email address, either through provider verification or trusted immutable provisioning.

This advisory covers the shared Passport profile normalization path when the selected profile email itself carries verified: false, when a matching raw provider email carries email_verified: false, or when an email obtained only from an ID token carries email_verified: false. It does not apply verification metadata from a different address or from a separate ID token to an independently fetched provider-profile email.