CVE-2026-53951

Copier is a library and CLI app for rendering project templates. In versions 9.5.0 through 9.15.1, the trust setting's prefix match (copier/_settings.py) compares the template URL against a trusted prefix with a raw str.startswith and no path normalization, while the URL is normalized when the template is actually fetched (Path.resolve() for local paths; libcurl dot-segment removal for https). A template reference that textually starts with a trusted prefix but contains .. is therefore granted trust yet resolves to a different, attacker-controlled template, whose tasks / migrations / jinja_extensions then run without the --trust prompt — arbitrary command execution. Version 9.15.2 patches the issue.