Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, Copier suggests that its safe to generate a project from a safe template, i.e. one that doesnt 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 users write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.
Weakness
The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Copier | Copier-org | * | 9.11.2 (excluding) |
Potential Mitigations
- Follow the principle of least privilege when assigning access rights to entities in a software system.
- Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.