CVE-2026-32235: @backstage/plugin-auth-backend OAuth Redirect URI Allowlist Bypass Vulnerability

MODERATE
Advisory Identifier: GHSA-wqvh-63mv-9w92
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CVSS 5.9
CWE-20 CWE-601
Published
Advisory Summary

CVE-2026-32235 is a MODERATE (CVSS 5.9) oauth redirect uri allowlist bypass vulnerability (CWE-20: Improper Input Validation) affecting @backstage/plugin-auth-backend libraries in the npm ecosystem. The issue involves oauth redirect uri allowlist bypass. Remediation is available by upgrading affected packages to version 0.27.1.

CVE-2026-32235 at a Glance

CVE Identifier CVE-2026-32235
GHSA Identifier GHSA-wqvh-63mv-9w92
Severity MODERATE
CVSS v3.1 Base Score 5.9
CWE Classification CWE-20: Improper Input Validation
Affected Product @backstage/plugin-auth-backend
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 5.9

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:R/S:U/C:H/I:L/A:N).

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

How to Fix CVE-2026-32235

To remediate this vulnerability, upgrade all affected @backstage/plugin-auth-backend 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-auth-backend fixed: 0.27.1 
npm install @backstage/plugin-auth-backend@0.27.1
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-auth-backend

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-32235, inspect your project dependencies using npm:

npm ls @backstage/plugin-auth-backend

Analyze the terminal output to locate any version of @backstage/plugin-auth-backend in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.27.1), your application is affected.

Note: The npm ls @backstage/plugin-auth-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-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In @backstage/plugin-auth-backend, 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 The experimental OIDC provider in `@backstage/plugin-auth-backend` is vulnerable to a redirect URI allowlist bypass. Instances that have enabled experimental Dynamic Client Registration or Client ID Metadata Documents and configured `allowedRedirectUriPatterns` are affected. A specially crafted redirect URI can pass the allowlist validation while resolving to an attacker-controlled host. If a victim approves the resulting OAuth consent request, their authorization code is sent to the attacker, who can exchange it for a valid access token. This requires victim interaction and that one of the experimental features is explicitly enabled, which is not the default. ### Patches Upgrade to `@backstage/plugin-auth-backend` version 0.27.1 or later. ### Workarounds Disable experimental Dynamic Client Registration and Client ID Metadata Documents features if they are not required. ### References - [RFC 6749 Section 3.1.2 - Redirection Endpoint](https://datatracker.ietf.org/doc/html/rfc6749#section-3.1.2)

CVE-2026-32235 Affected @backstage/plugin-auth-backend Versions

1 component(s)
Fixed Versions:
0.27.1
Product / Package Ecosystem Affected Versions Fixed Version
@backstage/plugin-auth-backend
npm/@backstage/plugin-auth-backend
npm
< 0.27.1
0.27.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/backstage/backstage/security/advisories/GHSA-wqvh-63mv-9w92
NVD — CVE-2026-32235 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-32235
Security Fix Commit FIX COMMIT
https://github.com/backstage/backstage/commit/6042dd0c7f0706e0f473dafa92799ecf19c825ec
@backstage/plugin-auth-backend Source Repository REPOSITORY
https://github.com/backstage/backstage

Frequently Asked Questions

What is CVE-2026-32235?
CVE-2026-32235 is a security vulnerability in @backstage/plugin-auth-backend involving OAuth redirect URI allowlist bypass under CWE-20: Improper Input Validation.
Which @backstage/plugin-auth-backend versions are affected?
Affected versions include releases prior to 0.27.1 across affected packages: @backstage/plugin-auth-backend.
What version fixes CVE-2026-32235?
Upgrading to 0.27.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @backstage/plugin-auth-backend affected?
Yes, @backstage/plugin-auth-backend is affected in releases prior to 0.27.1. Upgrade your dependency to 0.27.1 or later.
What is the CVSS score of CVE-2026-32235?
CVE-2026-32235 has a CVSS v3.1 base score of 5.9 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N.
What CWE is associated with CVE-2026-32235?
CVE-2026-32235 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check npm dependencies for CVE-2026-32235?
Run the dependency tree command: 'npm ls @backstage/plugin-auth-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-wqvh-63mv-9w92",
  "modified" : "2026-03-13T13:35:42Z",
  "published" : "2026-03-12T14:50:59Z",
  "aliases" : [ "CVE-2026-32235" ],
  "summary" : "@backstage/plugin-auth-backend: OAuth redirect URI allowlist bypass",
  "details" : "### Impact\n\nThe experimental OIDC provider in `@backstage/plugin-auth-backend` is vulnerable to a redirect URI allowlist bypass. Instances that have enabled experimental Dynamic Client Registration or Client ID Metadata Documents and configured `allowedRedirectUriPatterns` are affected.\n\nA specially crafted redirect URI can pass the allowlist validation while resolving to an attacker-controlled host. If a victim approves the resulting OAuth consent request, their authorization code is sent to the attacker, who can exchange it for a valid access token.\n\nThis requires victim interaction and that one of the experimental features is explicitly enabled, which is not the default.\n\n### Patches\n\nUpgrade to `@backstage/plugin-auth-backend` version 0.27.1 or later.\n\n### Workarounds\n\nDisable experimental Dynamic Client Registration and Client ID Metadata Documents features if they are not required.\n\n### References\n\n- [RFC 6749 Section 3.1.2 - Redirection Endpoint](https://datatracker.ietf.org/doc/html/rfc6749#section-3.1.2)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@backstage/plugin-auth-backend"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.27.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/security/advisories/GHSA-wqvh-63mv-9w92"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-32235"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/commit/6042dd0c7f0706e0f473dafa92799ecf19c825ec"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/backstage/backstage"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-601" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-12T14:50:59Z",
    "nvd_published_at" : "2026-03-12T19:16:17Z"
  }
}