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CVE-2025-55214 — Copier safe template has filesystem write access outside destination path

Affected: copier-org copier

Copier library and CLI app for rendering project templates. From 7.1.0 to before 9.9.1, 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 parent path or an absolute path. Constructing such paths is possible using Copier's builtin pathjoin Jinja filter and its builtin _copier_conf.sep variable, which is the platform-native path separator. 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. This vulnerability is fixed in 9.9.1.

GHSA-p7q8-grrj-3m8w — Copier's safe template has filesystem write access outside destination path

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 write files outside the destination path where a project shall be generated or updated. This is possible when rendering a [generated directory structure](https://copier.readthedocs.io/en/stable/configuring/#generating-a-directory-structure) whose rendered path is either a relative parent path or an absolute path. Constructing such paths is possible using Copier's builtin `pathjoin` Jinja filter and its builtin `_copier_conf.sep` variable, which is the platform-native path separator. 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.

#### Write access via generated relative path

Reproducible example:

```shell echo "foo" > forbidden.txt mkdir src/ echo "bar" > "src/{{ pathjoin('..', 'forbidden.txt') }}" uvx copier copy src/ dst/ cat forbidden.txt ```

#### Write access via generated absolute path

Reproducible example:

- POSIX:

```shell # Assumption: The current working directory is `/tmp/test-copier-vulnerability/` echo "foo" > forbidden.txt mkdir src/ echo "bar" > "src/{{ pathjoin(_copier_conf.sep, 'tmp', 'test-copier-vulnera…

PYSEC-2026-1273 — Copier's safe template has filesystem write access outside destination path

Affected: PyPI: copier

### Impact

#### Write access via generated relative path

Reproducible example:

```shell echo "foo" > forbidden.txt mkdir src/ echo "bar" > "src/{{ pathjoin('..', 'forbidden.txt') }}" uvx copier copy src/ dst/ cat forbidden.txt ```

#### Write access via generated absolute path

Reproducible example:

- POSIX: