Описание
Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true
Impact
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. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc.
[!NOTE]
At the time of writing, the exploit is non-deterministic, as Copier walks the template's file tree using
os.scandirwhich yields directory entries in arbitrary order.
Reproducible example (may or may not work depending on directory entry yield order):
Patches
n/a
Workarounds
n/a
References
n/a
Пакеты
copier
< 9.11.2
9.11.2
Связанные уязвимости
Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, 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. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.