Backstage: Improper validation of MkDocs plugin configuration in TechDocs

Backstage is an open framework for building developer portals. From 0.11.12 until 1.14.7 and 1.15.5, the @backstage/plugin-techdocs-node package is affected by improper validation of mkdocs plugin configuration in techdocs. An authenticated attacker with control over a TechDocs source repository could cause a documentation build to retrieve and publish data from network locations reachable by the build environment. Exposure depends on deployment topology, build mode, and target endpoint protections. Modern cloud metadata services that require tokens or special headers are not directly accessible through the affected behavior. This issue is fixed in @backstage/plugin-techdocs-node versions 1.14.7 and 1.15.5.