EUVD-2026-93990Published

Backstage: Insufficient audience validation in the Cloudflare Access auth provider

Collected exploitation and prediction evidence

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2026-106457

Published

Backstage is an open framework for building developer portals. From 0.1.0 until 0.5.0, the @backstage/plugin-auth-backend-module-cloudflare-access-provider package is affected by insufficient audience validation in the cloudflare access auth provider. 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. This issue is fixed in version 0.5.0.

Source published: 6 Oct 2026 20:13:26 UTC
Source modified: 7 Oct 2026 15:09:19 UTC
Observed here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

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CVSS 3.1 · 6.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

euvd · EUVD-2026-93990

Published

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Oct 6, 2026, 8:13:26 PM

dateUpdated: Oct 7, 2026, 3:09:19 PM

Source published: Oct 6, 2026, 8:13:26 PM (timezone not stated)
Source modified: Oct 7, 2026, 3:09:19 PM (timezone not stated)
Observed here: 30 Oct 2026 01:52:16 UTC
Source terms: ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 6.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

nvd · CVE-2026-106457

Published

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Analyzed

Weakness classifications: CWE-287

Original publisher date fields

published: 2026-10-06T21:17:16.083

lastModified: 2026-10-27T20:48:50.790

2 source CPE criteria · context only

cpe:2.3:a:linuxfoundation:backstage\/plugin-auth-backend-module-cloudflare-access-provider:*:*:*:*:*:node.js:*:*
cpe:2.3:a:linuxfoundation:backstage:*:*:*:*:*:*:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published: 6 Oct 2026 21:17:16 UTC
Source modified: 27 Oct 2026 20:48:50 UTC
Observed here: 29 Oct 2026 05:48:21 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 6.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS 3.1 · [email protected] · Primary · 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

osv · GHSA-q333-f498-w2x7

Published

### 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 is available in [Backstage v1.55.0](https://github.com/backstage/backstage/releases/tag/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: ```yaml 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.

Source published: 7 Oct 2026 20:25:25 UTC
Source modified: 7 Oct 2026 20:30:04 UTC
Observed here: 24 Oct 2026 13:17:17 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

Publisher rating · MODERATE