Vulnerabilities in pkg:npm/@backstage/plugin-proxy-backend

PACKAGE
Advisory Identifier: GHSA-472h-9c5j-prrr
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Advisory Summary

CVE-2026-106456 is a MODERATE (CVSS 4.8) remote code execution vulnerability (CWE-863: Incorrect Authorization) affecting Backstage libraries in the npm ecosystem. The issue involves inconsistent credential enforcement for overlapping proxy routes. Remediation is available by upgrading affected packages to version 0.6.18.

2 Known Advisory Record(s)
Package Vulnerability Intelligence

pkg:npm/@backstage/plugin-proxy-backend

2 Known Advisory Record(s)

Vulnerability advisories affecting package pkg:npm/@backstage/plugin-proxy-backend. Select an advisory below to view technical details or fixes.

Advisory ID CVE / NVD Severity Summary
GHSA-472h-9c5j-prrr CVE-2026-106456 MODERATE Backstage: Inconsistent credential enforcement for overlapping proxy routes
GHSA-9ghw-48h5-v2w5 CVE-2026-106491 MODERATE Backstage: Improper input validation in proxy-backend

CVE-2026-106456 at a Glance

CVE Identifier CVE-2026-106456
GHSA Identifier GHSA-472h-9c5j-prrr
Severity MODERATE
CVSS v3.1 Base Score 4.8
CWE Classification CWE-863: Incorrect Authorization
Affected Product Backstage
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 4.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-106456

To remediate this vulnerability, upgrade all affected Backstage dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@backstage/plugin-proxy-backend fixed: 0.6.18 
npm install @backstage/plugin-proxy-backend@0.6.18
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls @backstage/plugin-proxy-backend

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-106456, inspect your project dependencies using npm:

npm ls @backstage/plugin-proxy-backend

Analyze the terminal output to locate any version of Backstage in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.6.18), your application is affected.

Note: The npm ls @backstage/plugin-proxy-backend command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-863: Incorrect Authorization, where the product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. In Backstage, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact An operator can configure overlapping proxy paths with different credential requirements. When a parent path permits unauthenticated access and a nested path requires credentials, the parent exemption can also cover requests handled by the nested proxy. An unauthenticated caller may therefore reach the nested upstream through Backstage, including with static upstream credentials configured for that proxy. Exploitation requires this specific overlapping route configuration. The resulting confidentiality and integrity impact depends on the capabilities exposed by the nested upstream. ### Patches Upgrade `@backstage/plugin-proxy-backend` to version `0.6.18` or later. The fixed package is available in [Backstage v1.55.0](https://github.com/backstage/backstage/releases/tag/v1.55.0). ### Workarounds - Avoid nesting a credential-protected proxy path below a path configured with `dangerously-allow-unauthenticated`. - Apply the same credential requirement to overlapping proxy paths. - Restrict direct network access to the Backstage backend until the patched package is deployed.

CVE-2026-106456 Affected Backstage Versions

1 component(s)
Fixed Versions:
0.6.18
Product / Package Ecosystem Affected Versions Fixed Version
@backstage/plugin-proxy-backend
npm/@backstage/plugin-proxy-backend
npm
≥ 0.5.0
< 0.6.18
0.6.18

References

GitHub Advisory / Wiki ADVISORY
https://github.com/backstage/backstage/security/advisories/GHSA-472h-9c5j-prrr
NVD — CVE-2026-106456 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-106456
Security Fix Commit FIX COMMIT
https://github.com/backstage/backstage/commit/9df92923ac32558bb80edeceafd8de780c44e218
Backstage Source Repository REPOSITORY
https://github.com/backstage/backstage
Backstage Release RELEASE
https://github.com/backstage/backstage/releases/tag/v1.55.0

Frequently Asked Questions

What is CVE-2026-106456?
CVE-2026-106456 is a security vulnerability in Backstage involving Inconsistent credential enforcement for overlapping proxy routes under CWE-863: Incorrect Authorization.
Which Backstage versions are affected?
Affected versions include releases prior to 0.6.18 across affected packages: @backstage/plugin-proxy-backend.
What version fixes CVE-2026-106456?
Upgrading to 0.6.18 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @backstage/plugin-proxy-backend affected?
Yes, @backstage/plugin-proxy-backend is affected in releases prior to 0.6.18. Upgrade your dependency to 0.6.18 or later.
What is the CVSS score of CVE-2026-106456?
CVE-2026-106456 has a CVSS v3.1 base score of 4.8 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N.
What CWE is associated with CVE-2026-106456?
CVE-2026-106456 is classified under CWE-863: Incorrect Authorization (The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.).
How can I check npm dependencies for CVE-2026-106456?
Run the dependency tree command: 'npm ls @backstage/plugin-proxy-backend'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-472h-9c5j-prrr",
  "modified" : "2026-10-07T20:25:13Z",
  "published" : "2026-10-07T20:25:13Z",
  "aliases" : [ "CVE-2026-106456" ],
  "summary" : "Backstage: Inconsistent credential enforcement for overlapping proxy routes",
  "details" : "### Impact\n\nAn operator can configure overlapping proxy paths with different credential requirements. When a parent path permits unauthenticated access and a nested path requires credentials, the parent exemption can also cover requests handled by the nested proxy. An unauthenticated caller may therefore reach the nested upstream through Backstage, including with static upstream credentials configured for that proxy.\n\nExploitation requires this specific overlapping route configuration. The resulting confidentiality and integrity impact depends on the capabilities exposed by the nested upstream.\n\n### Patches\n\nUpgrade `@backstage/plugin-proxy-backend` to version `0.6.18` or later. The fixed package is available in [Backstage v1.55.0](https://github.com/backstage/backstage/releases/tag/v1.55.0).\n\n### Workarounds\n\n- Avoid nesting a credential-protected proxy path below a path configured with `dangerously-allow-unauthenticated`.\n- Apply the same credential requirement to overlapping proxy paths.\n- Restrict direct network access to the Backstage backend until the patched package is deployed.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@backstage/plugin-proxy-backend"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.5.0"
      }, {
        "fixed" : "0.6.18"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/security/advisories/GHSA-472h-9c5j-prrr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-106456"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/commit/9df92923ac32558bb80edeceafd8de780c44e218"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/backstage/backstage"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/releases/tag/v1.55.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-07T20:25:13Z",
    "nvd_published_at" : "2026-10-06T21:17:15Z"
  }
}