AIKIDO-2026-944819

TL;DR

When flatpak build-init is run with --sdk-extensions or --base-extensions, it copies extension files into the build directory using a target path taken from the directory key in the extension metadata, resolved with an API that follows .. components. A malicious SDK that declares an extension point with a crafted directory value can cause files to be written outside the build tree, and existing files at the traversed path are deleted and replaced. This lets a crafted SDK write to arbitrary locations in the developer's host context. The fix uses fd-relative operations to prevent path traversal during extension copying.