@backstage/plugin-auth-backend: OAuth redirect URI allowlist bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-32235: 0.15% estimated exploitation activity in the next 30 days; percentile 4.02 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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

Published by the source

12 Mar 2026, 14:50 UTC

Last modified by the source

14 Mar 2026, 01:56 UTC

Source last checked

26 Oct 2026, 12:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wqvh-63mv-9w92

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wqvh-63mv-9w92

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# Patch Next advisory brief: CVE-2026-32235

Advisory: @backstage/plugin-auth-backend: OAuth redirect URI allowlist bypass
IDs: CVE-2026-32235, GHSA-wqvh-63mv-9w92
Record: https://patchnext.com/advisories/cve-2026-32235 (revision 2, source checked 26 Oct 2026, 12:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @backstage/plugin-auth-backend 0.27.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @backstage/plugin-auth-backend: affected < 0.27.1; fixed in 0.27.1

## Suggested inspection (read-only)
- `npm ls @backstage/plugin-auth-backend --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @backstage/plugin-auth-backend.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wqvh-63mv-9w92 (OSV record GHSA-wqvh-63mv-9w92 lists affected ranges: npm @backstage/plugin-auth-backend >=0 <0.27.1 (fixed))
- Verified: https://github.com/advisories/GHSA-wqvh-63mv-9w92 (GitHub-reviewed advisory GHSA-wqvh-63mv-9w92 lists affected ranges: npm @backstage/plugin-auth-backend >=0 <0.27.1)

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