Affected: copier-org copier

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 include arbitrary files/directories outside the local template clone location by using symlinks along with `_preserve_symlinks: false` (which is Copier's default setting). Version 9.11.2 patches the issue.

Affected: PyPI: copier

### Impact

Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use [unsafe](https://copier.readthedocs.io/en/stable/configuring/#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`](https://copier.readthedocs.io/en/stable/configuring/#preserve_symlinks) (which is Copier's default setting).

Imagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations and hopes for a user to push the generated project to a public location like [github.com](https://github.com/) where the template author can extract the secrets.

Reproducible example:

- Illegally include a file in the generated project via symlink resolution:

```shell echo "s3cr3t" > secret.txt

mkdir src/ pushd src/ ln -s ../secret.txt stolen-secret.txt popd

uvx copier copy src/ dst/

cat dst/stolen-secret.txt #s3cr3t ```

- Illegally include a directory in the generated project via symlink resolution:

```shell mkdir secrets/ pushd secrets/ echo "s3cr3t" > secret.txt popd

mkdir src/ pushd src/ ln -s ../secrets stolen-secrets popd

uvx copier copy src/ dst/

tree dst/ # dst/ # └── stolen-se…

Affected: PyPI: copier

### Impact

Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use [unsafe](https://copier.readthedocs.io/en/stable/configuring/#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`](https://copier.readthedocs.io/en/stable/configuring/#preserve_symlinks) (which is Copier's default setting).

Imagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations and hopes for a user to push the generated project to a public location like [github.com](https://github.com/) where the template author can extract the secrets.

Reproducible example:

- Illegally include a file in the generated project via symlink resolution:

```shell echo "s3cr3t" > secret.txt

mkdir src/ pushd src/ ln -s ../secret.txt stolen-secret.txt popd

uvx copier copy src/ dst/

cat dst/stolen-secret.txt #s3cr3t ```

- Illegally include a directory in the generated project via symlink resolution:

```shell mkdir secrets/ pushd secrets/ echo "s3cr3t" > secret.txt popd

mkdir src/ pushd src/ ln -s ../secrets stolen-secrets popd

uvx copier copy src/ dst/

tree dst/ # dst/ # └── stolen-se…