Copier's _subdirectory setting is documented as the subdirectory to use as the template root. However, the current implementation accepts parent-directory traversal such as .. and uses it directly when selecting the template root. As a result, a template can escape its own directory and make Copier render files from the parent directory without –UNSAFE.
Copier's _external_data feature allows a template to load YAML files using template-controlled paths. The documentation describes these values as relative paths from the subproject destination, so relative paths themselves appear to be part of the intended feature model. However, the current implementation also allows destination-external reads, including: Parent-directory paths such as ../secret.yml Absolute paths such as /tmp/secret.yml and then exposes the parsed contents in rendered output. This is possible without …
Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the –UNSAFE,–trust flag. As it turns out, a safe template can currently write to arbitrary directories outside the destination path by using directory a symlink along with _preserve_symlinks: true and a generated directory structure whose rendered path is inside the symlinked directory. …
Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the –UNSAFE,–trust flag. As it turns out, a safe template can currently include arbitrary files/directories outside the local template clone location by using symlinks along with _preserve_symlinks: false (which is Copier's default setting). Imagine, e.g., a malicious template author who creates a …
Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the –UNSAFE,–trust flag. As it turns out, a safe template can currently write files outside the destination path where a project shall be generated or updated. This is possible when rendering a generated directory structure whose rendered path is either a relative …
Copier's current security model shall restrict filesystem access through Jinja: Files can only be read using {% include … %}, which is limited by Jinja to reading files from the subtree of the local template clone in our case. Files are written in the destination directory according to their counterparts in the template. Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't …