vulnerability / NVI-00012018 / Revision 3
Backstage: Insufficient audience validation in the Cloudflare Access auth provider
GitHub lists this reviewed advisory for @backstage/plugin-auth-backend-module-cloudflare-access-provider. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.8 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
6.8 MEDIUM (3.1)
security-advisories@github.com severity; no combined Null risk score.
8.1 HIGH (3.1)
nvd@nist.gov severity; no combined Null risk score.
0.281%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.20635. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
@backstage/plugin-auth-backend-module-cloudflare-access-provider
source listed>= 0.1.0, < 0.5.0
### Impact 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
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-q333-f498-w2x7 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-106457 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-106457 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.