Backstage OIDC auth plugin: Improper authentication via unverified email addresses
Summary
The OIDC provider module of Backstage, an open framework for developer portals, resolves identities by email address. If the identity provider permits unverified email addresses, an authenticated provider user can assume another catalog identity and gain that identity's access and permissions. The CVSS score is 8.1 (High), and no direct availability impact has been demonstrated. Exploitation requires a valid account at the identity provider and email-based sign-in resolution.
Affected
- @backstage/plugin-auth-backend-module-oidc-provider before 0.4.20
- Backstage core (backstage) before 1.54.6, per the official CVE record
Fixed in
- @backstage/plugin-auth-backend-module-oidc-provider 0.4.20
- Backstage v1.54.6 (release that includes the fix)
Workaround
- Disable email-based sign-in resolution for the OIDC provider, or
- require the identity provider to verify email addresses before sign-in is allowed.
Exploitation
- No public reports of active exploitation found.
- CISA SSVC assessment: exploitation none, automatable no, technical impact total.
- No public proof of concept verified.
Our recommendation
- Check whether Backstage and this plugin are deployed, for example in lockfiles and deployment manifests.
- Update the plugin to 0.4.20 or later and Backstage to v1.54.6 or later.
- Confirm that the identity provider only allows verified email addresses for sign-in.
- Until the update is applied, disable email-based identity resolution or review catalog entries that resolve identities by email.
- Review access granted to catalog identities for unexpected changes.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-826h-28h9-65hg github.com
- Fix commit 1b1f05e: validate OIDC profile email claims github.com
- Backstage release v1.54.6 github.com
- OSV: GHSA-826h-28h9-65hg osv.dev
- OSV: CVE-2026-106488 osv.dev
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 20:41.
Original description (NVD)
Backstage is an open framework for building developer portals. Prior to 0.4.20, the @backstage/plugin-auth-backend-module-oidc-provider package is affected by improper authentication in the oidc provider. Deployments using OIDC email-based identity resolution with a provider that permits unverified email addresses may allow an authenticated provider user to assume another catalog identity. This may grant access and permissions associated with that user. No direct availability impact is demonstrated. This issue is fixed in version 0.4.20.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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