Backstage: Improper validation of MkDocs theme configuration in TechDocs

Exploitation

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

CVSS

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

EPSS

• CVE-2026-106509: 0.52% estimated exploitation activity in the next 30 days; percentile 44.00 (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 When TechDocs is configured to build documentation locally or in a container, a user with write access to a registered repository can include configuration values in mkdocs.yml that cause arbitrary code execution during the documentation build process. Patches Patched in @backstage/plugin-techdocs-node version 1.15.4 Workarounds - Configure TechDocs with techdocs.generator.runIn: 'docker' instead of 'local' to provide container isolation, though this does not fully mitigate the risk. - Restrict write access to repositories registered in the Backstage catalog to trusted users.

Published by the source

7 Oct 2026, 16:23 UTC

Last modified by the source

7 Oct 2026, 16:30 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8w7q-29mw-gf5c

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-8w7q-29mw-gf5c

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-8w7q-29mw-gf5c

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-106509

Advisory: Backstage: Improper validation of MkDocs theme configuration in TechDocs
IDs: CVE-2026-106509, GHSA-8w7q-29mw-gf5c
Record: https://patchnext.com/advisories/cve-2026-106509 (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 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @backstage/plugin-techdocs-node 1.15.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @backstage/plugin-techdocs-node: affected < 1.15.4; fixed in 1.15.4

## Suggested inspection (read-only)
- `npm ls @backstage/plugin-techdocs-node --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-techdocs-node.
- 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-8w7q-29mw-gf5c (GitHub-reviewed advisory GHSA-8w7q-29mw-gf5c lists affected ranges: npm @backstage/plugin-techdocs-node >=0 <1.15.4)
- Verified: https://osv.dev/vulnerability/GHSA-8w7q-29mw-gf5c (OSV record GHSA-8w7q-29mw-gf5c lists affected ranges: npm @backstage/plugin-techdocs-node >=0 <1.15.4 (fixed))

Commands are suggestions: review each one before running it.