Backstage: Scaffolder action input authorization bypass

Exploitation

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

CVSS

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

EPSS

• CVE-2026-106503: 0.49% estimated exploitation activity in the next 30 days; percentile 42.34 (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 An authenticated user with access to affected Scaffolder templates could bypass configured action restrictions. Depending on integration credentials, this could grant unauthorized access to repositories and related source-control resources. Patches Patched in @backstage/plugin-scaffolder-backend version 4.1.0 Workarounds - Restrict affected Scaffolder actions to trusted users and configure source-control integrations with least-privilege credentials.

Published by the source

7 Oct 2026, 17:59 UTC

Last modified by the source

7 Oct 2026, 18:15 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-hmp2-4m7g-22cv

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-hmp2-4m7g-22cv

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-hmp2-4m7g-22cv

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# Patch Next advisory brief: CVE-2026-106503

Advisory: Backstage: Scaffolder action input authorization bypass
IDs: CVE-2026-106503, GHSA-hmp2-4m7g-22cv
Record: https://patchnext.com/advisories/cve-2026-106503 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @backstage/plugin-scaffolder-backend 4.1.0, 4.0.3, 3.4.1, 3.3.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @backstage/plugin-scaffolder-backend: affected < 3.3.1; >= 3.4.0, < 3.4.1; >= 4.0.0, < 4.0.3; >= 4.0.4, < 4.1.0; fixed in 3.3.1, 3.4.1, 4.0.3, 4.1.0

## Suggested inspection (read-only)
- `npm ls @backstage/plugin-scaffolder-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-scaffolder-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://github.com/advisories/GHSA-hmp2-4m7g-22cv (GitHub-reviewed advisory GHSA-hmp2-4m7g-22cv lists affected ranges: npm @backstage/plugin-scaffolder-backend >=0 =3.4.0 =4.0.0 =4.0.4 <4.1.0)
- Verified: https://osv.dev/vulnerability/GHSA-hmp2-4m7g-22cv (OSV record GHSA-hmp2-4m7g-22cv lists affected ranges: npm @backstage/plugin-scaffolder-backend >=0 =3.4.0 =4.0.0 =4.0.4 <4.1.0 (fixed))

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