Vulnerability-Lookup

GHSA-Q333-F498-W2X7

Vulnerability from github – Published: 2026-10-07 20:25 – Updated: 2026-10-07 20:25

Summary

Backstage: Insufficient audience validation in the Cloudflare Access auth provider

Details

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.

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.

Severity

6.8 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@backstage/plugin-auth-backend-module-cloudflare-access-provider"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.1.0"
            },
            {
              "fixed": "0.5.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-106457"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-07T20:25:25Z",
    "nvd_published_at": "2026-10-06T21:17:16Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nThe Cloudflare Access auth provider verifies a token\u0027s 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\u0027s audience already being enforced upstream.\n\nCloudflare 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.\n\nA successful sign-in also depends on the deployment\u0027s sign-in resolver mapping the presented identity to a Backstage user. The resulting impact depends on the permissions assigned to that identity.\n\n### Patches\n\nUpgrade `@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).\n\nThis 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:\n\n```yaml\nauth:\n  providers:\n    cfaccess:\n      teamName: example\n      audience: ${AUTH_CFACCESS_AUDIENCE}\n```\n\n### Workarounds\n\n- Restrict access to the Backstage auth endpoint to the intended Cloudflare Access application.\n- Use a custom authenticator that validates the application audience.\n- Disable the provider until the patched package can be deployed.",
  "id": "GHSA-q333-f498-w2x7",
  "modified": "2026-10-07T20:25:25Z",
  "published": "2026-10-07T20:25:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/security/advisories/GHSA-q333-f498-w2x7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-106457"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/commit/ed9034cacd9def3b3674f0a764fe992f751e204d"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/backstage/backstage"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/releases/tag/v1.55.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Backstage: Insufficient audience validation in the Cloudflare Access auth provider"
}

CVE-2026-106457 (GCVE-0-2026-106457)

Vulnerability from cvelistv5 – Published: 2026-10-06 20:13 – Updated: 2026-10-07 15:09

Title

Backstage: Insufficient audience validation in the Cloudflare Access auth provider

Summary

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.

Severity

6.8 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-07 15:06 UTC

CWE

CWE-287 - Improper Authentication

Assigner

GitHub_M mitre root Scorecard

References

3 references

URL	Tags
https://github.com/backstage/backstage/security/a…	x_refsource_CONFIRM
https://github.com/backstage/backstage/commit/ed9…	x_refsource_MISC
https://github.com/backstage/backstage/releases/t…	x_refsource_MISC

Impacted products

2 products

Vendor	Product	Version
backstage	backstage	Affected: >= 1.26.0, < 1.55.0
@backstage	plugin-auth-backend-module-cloudflare-access-provider	Affected: >= 0.1.0, < 0.5.0

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-106457",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-07T15:06:22.900061Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-07T15:09:19.708Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "backstage",
          "vendor": "backstage",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.26.0, \u003c 1.55.0"
            }
          ]
        },
        {
          "product": "plugin-auth-backend-module-cloudflare-access-provider",
          "vendor": "@backstage",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.1.0, \u003c 0.5.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u0027s 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\u0027s audience already being enforced upstream. Cloudflare Access normally evaluates the protected application before forwarding requests. This issue is fixed in version 0.5.0."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 6.8,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-287",
              "description": "CWE-287: Improper Authentication",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-06T20:13:26.801Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/backstage/backstage/security/advisories/GHSA-q333-f498-w2x7",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/backstage/backstage/security/advisories/GHSA-q333-f498-w2x7"
        },
        {
          "name": "https://github.com/backstage/backstage/commit/ed9034cacd9def3b3674f0a764fe992f751e204d",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/backstage/backstage/commit/ed9034cacd9def3b3674f0a764fe992f751e204d"
        },
        {
          "name": "https://github.com/backstage/backstage/releases/tag/v1.55.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/backstage/backstage/releases/tag/v1.55.0"
        }
      ],
      "source": {
        "advisory": "GHSA-q333-f498-w2x7",
        "discovery": "UNKNOWN"
      },
      "title": "Backstage: Insufficient audience validation in the Cloudflare Access auth provider"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-106457",
    "datePublished": "2026-10-06T20:13:26.801Z",
    "dateReserved": "2026-10-06T16:49:40.591Z",
    "dateUpdated": "2026-10-07T15:09:19.708Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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