CVE-2026-106505: Backstage: Bypass of MkDocs configuration sanitizer in TechDocs backend

### Impact Users with the ability to commit changes to a repository that uses TechDocs can circumvent the MkDocs configuration file sanitizer introduced in response to CVE-2026-25153 and execute arbitrary code on the TechDocs backend host during documentation generation. ### Patches Patched in`@backstage/plugin-techdocs-node` version `1.15.4` ### Workarounds If you cannot upgrade immediately: - Use Docker mode with restricted access: Configure TechDocs with `runIn: docker` instead of `runIn: local`. This provides container isolation, though it does not fully mitigate the risk. - Limit repository write access to trusted parties, since exploitation requires the ability to commit files to a repository with TechDocs enabled. - Review incoming changes to MkDocs configuration files as part of your code review process.